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1] Run Disk Cleanup from Start > All programs > Accessories > System Tools > Disk Cleanup.
After the initial, sometimes slow, compressed file check, the main window appears with two tabs. Disk Cleanup is the normal one everyone uses, but the 2nd tab, "More Options", has the useful option of "System Restore". This allows you to remove all but the latest System Restore point backup files. That is what the _Restore hidden folder holds.
2] Disable System Restore, then re-enable it immediately.
Find your My Computer icon, right click it and select Properties. In the System Restore tab, select "Turn off System Restore", click Apply/OK, then return, and re-enable it.