If you have the system recovery media set for this computer, boot off of the CD and at the menu where it asks you what type of recovery you want to perform, there should be an option to tell it to wipe all data and set it back to factory. This will format the hard drive and install Windows 95 fresh to the system, so that you can sell it with Windows 95 running on it.
If you dont have the recovery media then you will need a bootable floppy or CD and then booted off of this media perform the Format C: where the Format command is located on the Floppy or CD and from the A: prompt if a Floppy or from the D: or E: prompt ( whatever your CD ROM is mapped as ) run the format instruction from there to format the C: drive.