- Click the Windows "Start" button and click the "Control Panel."
- Click on "Programs" in the Control Panel and then click on "Programs and Features." You will see a list of screensavers installed on your computer.
- Scroll through and click the screensaver you want to delete. Click "Uninstall" to remove it from your computer. 

Also you can delete the screensavers manually from the folders:

-for XP and Vista 32 go to C:/Windows/System32

-for Windows Vista 64 go to C:/Windows/SysWow64

and

-for all users C:\Program Files\NewFreeScreensavers

Note that the screensavers that come with Windows, however, can't be removed.

For Mac

Mac screensavers can be removed using the Screen Saver System preference panel: 

 - Select "System Preferences..." in the Apple menu. 

- Select the Desktop & Screen Saver panel. 

- Select the Screen Saver tab at the top of the panel. 

- Select the Screen Saver you wish to uininstall from the list of screensavers. 

- Click the "Options..." button and click the "Delete" button in the Options sheet.

The screensavers are stored in the /System/Library/Screen Savers/ folder. Third-party screen savers may be found in /Library/Screen Savers/ or in /Home/Library/Screen Savers/ folders.