How to change my desktop screen size back to normal?

I don't know what happened but now my screen have become smaller,not just the icons,but when i surf web,everything become smaller.How to change this?How to change my desktop screen size back to normal?
Right click on the screen and go to properties. Find screen resolution and click on it. On the list it will show a bunch of numbers, the lower the number the bigger the screen.How to change my desktop screen size back to normal?
on xp:

right click desktop and click properties



in vista and 7:

right click desktop and click perosnalize.



next time, use google.
Right click on your desktop background then go to Screen Resolution then click the drop down box after it says Resolution. This is how you do it in Windows 7.