I wanted to play some older mods on 1.6.4 so I downloaded Forge 1.6.4 from the official CurseForge website. When I downloaded it I realized that the mods I wanted to use were not in 1.6.4 but rather were in 1.7.10. I tried to delete the older version of Forge, but this proved to be impossible. There is no way to delete it. I can't delete it from the launcher screen(nor can I edit it in any way), so I went into %AppData% to delete it straight from the game files but even after I deleted the Forge 1.6.4 file from "versions", the option to select 1.6.4 from the launcher is still here and still impossible to delete. This has never happened to me before and I have no idea what to do. On my computer I also have Forge 1.12.2 downloaded and it runs as normal- I can delete it whenever I want to. Obviously I cannot launch this glitched version of 1.6.4 but I desperately would like to delete it. Please help?

(Edit: I just discovered a new problem. The launcher flat out refuses to run Forge 1.7.10. Even though it is downloaded from the proper website and the files are in the correct places, the launcher straight-out does not recognize it. It's not even an option on the versions selector menu. What is going on?)