Hai
 There are many ways to increase the computer speed like removing the unuse stuff, editing the startup, editing in the registry edit etc.
  In this blog i am going to use a hacking tool named speeder xp and this is the simple method

don't worry to search, here is the url   www.speederxp.com.
If you want to download, copy the above url and paste in the above google search box (top of the blog) and download. 
Download it from the above url and after installing it looks like this

 There are free version and pro versions those who want free version download all the free version and use one after the other .There are many versions

NOTE : Don't set the speed to the maximum because it uses the maximum process power it may work for a week or more but after that you may confront problem with the computer