Okay this has been covered multiple times on the forum and basically if you want to delete stuff from your ROM set its either as easy as can be or very difficult. Which it is depends on what type of ROM set you have if you have a split or merged set then its a PITA and really not something someone with extensive knowledge of MAME should even attempt, however if you have a Non-Merged ROM set then its pretty much easy as pie. The reason for the disparity is the way that the split and merged sets are set up vs the structure of the Non-Merged set. In the split set ever game and clone has its own file but some of those files are dependent on other files in the set. In a merged set only the parent of a game has its own file and the clones are contained inside of the parents but these are still dependent on other files such as system boards and bios files. Due to this if you remove files without knowing what you are doing you will in all likelihood remove files that are needed for some of the games you want to keep to work so like I said earlier if you don't know MAME very well this is not something to be doing. A Non-Merged set is setup just like a split set in that every game including clones have their own file except there is no dependencies on other files all files needed for the game to work are contained in each file. This is the reason that it is twice as large as the other sets. So now that I've explained that basically you can do what you want if you get a Non-Merged set they are available on Pleasuredome just Google Pleasuredome Roms and you will find the site.