How to edit a DVD of an officially released show that was released by official publishers

Hey all, so I recently got the original DVD release of South Park season 1 and, frankly, the DVD quality is worse than VHs. And I’m playing it on my CRT so I know its not an issue with modern TVs. However I have managed to get my hands on some better quality, fan-edited episodes and I was wondering- how am I able to edit the existing South Park DVDs to delete the old video files and insert the new ones? And if possible I want to add some extra videos as special features (e.g the original two shorts). I’m also looking to get into creating DVD menus from scratch as there is a fantastic Top Gear restoration project by AlexTGRF on Reddit which I want to be able to put onto DVD annd store in my collection

If its possible I’ll be doing this with Initial D too as it has both problems- no official releases and the release I have has crappy video and audio, which I intend to replace