How do I delete all of an old Mac's backups from my Time Capsule?

I have recently purchased a new Macbook Pro and used my Time Capsule to copy over the files from my iMac I wanted to keep (I didn't both with the apps, etc... just the documents, photos and music folders).

I'm going to format my old iMac clean and sell it on. I'd also like to start using my Time Capsule to backup the new MBP. But first I'd like to remove all the backup files from the TC rather than having 500 Gb of duplicated files remaining dormant as the original computer is gone (seeing as they are on the new MBP already). Given that I would have two separate computers, if I start getting low on space, then Time Machine wouldn't automatically delete the old backups of the old computer... so I just want to get rid of them.

There seems to be a number of different methods out there, each with its own warnings, etc... so I'm not sure what to do.

I don't mind reformating the TC to its original settings and starting from scratch if that's the best way, but not sure how to do that either.

Thanks!