Welcome to the all-new Windows Central Forums! - We're still moving some things around, so you may see a few quirks here and there, but we're working on getting things fully completed as soon as possible. For now, take a look around, and if you run into any major issues, please let us know in this thread!
I'm not aware of any way to remove things from the cloud collection, but here's a guide on using album match to add things. It's somewhat janky, but it does work for the most part.
http://winsupersite.com/xbox-music/xbox-music-feature-focus-album-match