(10-15-2015, 07:32 AM)kieranDavidWood234 Wrote: Is there any way to change the games music?
You need to modify the disc image to do that. (It can technically also be done the way Project M does it, but that's even harder...) You will need a program that can unpack and repack GameCube ISOs, and an encoder for the audio format that the game uses.
(10-15-2015, 07:32 AM)kieranDavidWood234 Wrote: And is there a way to increase the quality of the textures?
Dolphin supports files of any resolution (but they should preferably be larger than the original by an integer factor). Just put a high-res texture in the Load folder as described by the topic I linked to, and Dolphin will use the high-res texture.