Delete programs you never use
Many PC manufacturers pack their new computers with programs you didn’t order and might not want. These often include trial editions and limited edition versions of programs that software companies hope you will try, find useful, and then pay to upgrade to full versions or newer versions. If you decide you don’t want them, keeping the software on your computer might slow it down by using precious memory, disk space, and processing power.

It’s a good idea to uninstall all the programs you don’t plan to use. This should include both manufacturer-installed software and software you installed yourself but don’t want anymore—especially utility programs designed to help manage and tune your computer’s hardware and software. Utility programs such as virus scanners, disk cleaners, and backup tools often run automatically at startup, quietly chugging along in the background where you can’t see them. Many people have no idea they are even running.

Even if your PC is older, it might contain manufacturer-installed programs that you never noticed or have since forgotten about. It’s never too late to remove these and get rid of the clutter and wasted system resources. Maybe you thought you might use the software someday, but never did. Uninstall it and see if your PC runs faster.

Defragment your hard drive
Fragmentation makes your hard disk do extra work that can slow down your computer. Disk Defragmenter rearranges fragmented data so your hard disk can work more efficiently. Disk Defragmenter runs on a schedule, but you can also defragment your hard disk manually.

Add more memory
This isn’t a guide to buying hardware that will speed up your computer. But no discussion of how make Windows run faster would be complete without mentioning that you should consider adding more memory to your PC.
If a computer running Windows Vista feels too slow, it’s usually because the PC doesn’t have enough memory. The most sure–fire way to speed it up is to add more.

Windows Vista can run on a PC with 512 megabytes (MB) of random access memory (RAM), but it runs better with 1 gigabyte (GB). For optimal performance, boost that to 2 GB or more.
If you're going to the trouble of opening up your PC case to add more memory, you might as well boost the total to at least 2 GB. Especially if you're the sort of person who keeps a dozen e‑mail messages, ten browser windows, and six other programs open at once—all while instant messaging.

Check for viruses and spyware
If your PC is running slowly, one dreaded possibility is that it might be infected with a virus or spyware. This is not as common as the other problems, but it is something to consider. Before you worry too much, check your PC using antispyware and antivirus programs.

A common symptom of a virus is a much slower-than-normal computer performance. Other signs include unexpected messages that pop up on your PC, programs that start automatically, or the sound of your hard disk constantly working.
Spyware is a type of program that is installed, usually without your knowledge, to watch your activity on the Internet. You can check for spyware with Windows Defender or other anti-spyware programs. For more information, see How to tell if your computer is infected with spyware.