icloud has ruined my itunes libary

A few years ago I made the disastrous decision to activate my itunes into the cloud. I want to just get my library back to the way it was. The biggest issue is that itunes has replaced many of my favourite songs with garbage songs - live versions instead of the original studio recording I had. Alternate B artists have replaced my original artists. How can I restore my original library? I believe all the songs are still there. The other thing is I purchased ipads and iphones with big memory to store the songs on my devices because I travel outside of cell phone data access points. I would download my whole library in the past, and now I have to download selected songs, playlists etc. I want my whole library on my iphone and ipads which it used to do.