Will an upgrade help?
What's the thing that bugs you the most? Is it the fact that programs take a while to load? Or that it takes forever to boot your desktop? Does your PC start out fine but slows down once you've been using it for a while? If that's the case you should be able to upgrade a component or two and get on with your life. Let’s look at the upgrade options available to you…
If your system is slow starting up, slow performing day-to-day tasks, and slow shutting down, it's possible that your hard drive is full and needs paring down. Luckily, there's a quick and free fix for this. Uninstall programs you no longer use, delete extraneous video files, and if you're using Windows try running Disk Cleanup. This should release at least a couple of gigabytes of space, but it's better still if you have around a third of your hard drive's capacity free. This will probably just be a temporary fix, however – you'll most likely want to upgrade to a larger drive. If you're not up to installing a new one inside your computer, buy an external USB 3.0 drive (assuming your PC has a USB 3.0 port), move all your music, photo, and video files to it, and you should be okay.
Back in the old days of computing, when systems had tiny amounts of memory such as 64KB, you had to quit out of a program to open a new one. Now multitasking is the norm. Most four-year-old PCs have at least 2GB of memory, which is rather underpowered, although many will have 4GB which is decent enough. If you’re doing a lot of multi-tasking though, or you like to keep a hundred plus browser tabs open at once, then 8GB can be a very worthwhile upgrade.
Even if you have to "throw away" your existing desktop memory because of a shortage of slots, 8GB of memory can be purchased for as little as £35 or so. Installing memory is easy: If you can build an IKEA bookshelf, installing memory in a desktop PC should be a walk in the park. It’s just a simple matter of slotting it in, really.
Solid-state drives (SSDs) are based on flash memory rather than the platters of traditional hard drives, and will prove the most telling upgrade of all from a standard hard disk, offering speed benefits that may make you think you have a new PC under your desk. Installing an SSD is like installing any new hard drive: Find a free SATA port on the motherboard, connect the SATA data and power cables to the new drive, secure the drive in a free drive bay, and install the operating system on it. An SSD is so small that you can slip it into any drive bay with an adapter, even the one that was made to hold floppy drives.
The fact that you're installing a new OS from scratch (free from resource-sapping bloatware) will further boost your performance, but the SSD's inherent speed will make you a believer the first time your system boots up in less than 20 seconds. The time it takes to launch apps should drop from a painfully long wait to just a few seconds. SSD prices have come down these days, and they run from as little as £60 for a decent-size one (128GB), although the larger drives are still expensive. Again, when it comes to installation, the level of difficulty is relatively low, and you should be fine if you're comfortable turning a screwdriver.
Geek out or grab your wallet
If your system's hard drive has plenty of free space and your system is loaded with memory, and things still feel slow, you need to resort to more drastic measures. The tech savvy can drop in a faster processor or install a leaner operating system, but for most people the answer is a new computer.
Upgrade your CPU
Replacing a CPU is an involved undertaking that requires more than a simple plug-in. The process of cracking heat sinks, spreading thermal paste, and fiddling with the BIOS will take you quite some time if you've never done it before. At best you will have a system with a newer, faster processor. At worst you will have an out-of-warranty desktop that will never boot again (aka a brick). If you're feeling brave, though, you can have a crack at doing this yourself, but take your time, and be very careful.
Install an enthusiast OS
If you're willing to wade out a little further, another option is installing a version of Linux, and you can always plump for an "easy" build like Ubuntu or ChromeOS. ChromeOS feels quite fast on low-powered systems like the Samsung Series 3 Chromebox, so your PC from a few years ago should be more than powerful enough to run it. Note that you'll lose any Windows apps you're used to when switching OS, but if all you're doing is surfing the web, Chrome works fine. There are loads of versions of Linux out there, with varying degrees of support and updates. Who knows, you may commit to Linux after the experience and never want to buy another computer with Windows or OS X again.
Buy a new PC
When mulling the decision to buy, you may be tempted to look to the near future and think: "Isn't there going to be something better in six months?" My advice is that you should never put off a tech buy when you need an item. There will always be something better and faster six months from now, and in the meantime you will have been using something that's been "too slow" for those six months.
If your current PC is just starting to get slow but isn't unbearable yet, then an upgrade will most likely let you use it comfortably for another six months or a year. At the very least you'll have a few more months to save up for that new PC.