There are some simple ways to help eliminate this annoying burden, one being to simply run disk cleanup which will help you clean up many un-necessary files. You can find “disk cleanup” usually on your control panel in the maintenance section, or by going to start all programs accessories, then system tools, and finally clicking on disk clean up, if you can't find it you can always search your help for “disk cleanup” and your computer will lead you to it.
After running disk clean up you could also run “disk defragmenter” which is located in the same position as the “disk clean up” program. This will take and re-arrange the files on your computer to help it run more smoothly.
Of course, another alternative is to manually delete all unnecessary files you have stored on your computers…that being said, “un-necessary” could be anything from a program you haven't used in forever to that picture you mean to touch up but just haven't gotten to. It's not exactly the preferred solution, after all who wants to wade through all there stuff to determine what's junk and what's not?
The Best Solution
Now these methods all work yes, but it's not exactly the best thing in the world to have to do them every so many hours just to get your computer to run at a decent speed. The most optimum solution then, is to increase your computers actual memory size. There are a number of computer stores you can go to which will sell it. Most should also offer a service to install the memory as well, one which I know does offer this service is Best Buy, but there are surely others; you will simply have to bring the processor to them so they can install the memory.
Oh, and make sure that they run chkdsk /f every so often as well