For version 4 or higher, clear up the burner's temporary files by clicking "Preferences" from the "File" menu. Select "General" and then select "Delete Temporary Files".
Start "Disk Cleanup" by clicking the Windows Start menu, pointing to "Programs," pointing to "Accessories," pointing to "System Tools," and then clicking "Disk Cleanup." If you don"t have "Disk Cleanup", you may need to add it via the Add/Remove Control panel in your "Settings".
You may also need to manually drag some files to the "Recycle Bin". Don't forget to right click on the Recycle Bin and select "Empty Recycle Bin"
Finally, you may be able to uninstall programs you don't use often, especially games, which are notorious for taking up a lot of space.