Hi
The checkpoints can't be manually deleted, so you have a few options open to
you.
Either delete all of them by turning System Restore off/on or by using Disk
Cleanup to delete all but the last checkpoint:
Programs>Accessories>System Tools>Disk Cleanup.
Click on the 'More Options' tab, then 'Clean up...' on the third option.
A 3rd option is to decrease the amount of disk space made available to
System Restore:
Right click on My Computer, then select Properties>System Restore. Select
the appropriate drive and click on 'Settings'. You can use the slider to
decrease the amount of disk space used by SR. I have mine set to 300 mb
which gives me about 5/6 checkpoints