I have a wordpress account with one wordpress site on it

I have a wordpress account with one wordpress site on it right now (bakersspot.com). I would like to install wpmudev on my other site (bakerbins.com) so I can use the plugins… How do I do that?
On a side note, I also need help with this issue too that's complicated for me to explain… But here goes:
Bakerbins.com used to be bakerbins.wordpress.com but we finally got it hosted on one of our servers. How do I change the backend of that site so that I can edit it and instal wpmudev on it? I want to customize that site now that it is just a .com site. Are their more steps I have to do so I can do that? I am really new to all of this and would love a detailed answer. Thank you!