how to format external hd after you use it in the time machine ?

[Luigi Ventura]

installed my 500gb external hard drive (model WD External Media 5000BEV) to use it in the time machine on my macbook pro with mac osx system. Now I dont want the time machine anymore, i want to format it to use it at work. and the system complains: Could not unmount the disk . I've tried almost everything, I do not know what else to do. thanks in advance .

 

[ScoobyMcDoo]

I've tried almost everything,

If you tell us what "everything" is, it would be helpful.

But just in case this is not part of "everything", did you turn off time machine?