Cleaning up the multisite SQL database

I’ve had a good play with the multisite setup, creating new sites (as subdomains) and figuring out which cloner I want to use. Now that those decisions are made, I’d like to clean up the database from all those extra wp_2 (through wp_10) files. I’ve never touched the database before so I’m not sure what to do (apart from making a backup first!).

Can anyone give me some pointers? Is there a suitable plugin or should it be done manually?
Thanks.