Removing Vista from dual boot with Win8

Hi I have a Win8 / Vista dual boot - Win8 on SSD on C: and Vista on HDD on D: (data only on E: ) I have not used Vista since installing Win8 and now want to remove to free up some space and remove dual boot Is there an option to keep my files on the drive but simply remove the Vista OS folder and remove the dual boot option? Or do I need to follow process *here...