External Hard Drive

I ask this question at the risk of sounding completely foolish, but here goes.
I have a 80GB external hard drive. I have some things on it that are totally out of date and that I don't need, but also have some things that I want to keep or maybe reinstall. I'm wondering if I can format the external drive without causing other problems on my computer. The reason I ask is that I have noticed some newer programs that I have added to my main drive and don't know how they showed up on the external drive. I keep the external drive unplugged from the electric plugin, but leave it plugged to the USB plug-in on the computer. Should I keep it unplugged from the computer while not using it. I use it as a backup for music files,downloads,etc. I would like to just format it and start over if it is safe. Thanks in advance for any information about external hard drives.
Red

 

Thanks for the reply. My external drive did not come with any extra disks. It is just plug and play.It does not have an on-off switch and I don't need to use it that much so I leave it unplugged. When I get time, I'll do as you advised. I'll back up anything that I might need and then format the drive.
Thanks again,
Red

 

The backup program doesnt need to come on a disc it can be stored on the HD itself.