You can change the tilesets by replacing the TileA1, TileA2, TileA3, TileA4, TileA5, TileB, TileC, TileD, TileE files in the System Directory (use the Resource Manager is probably easiest)
E is the same as B, C, and D. Upper layer tiles that support transparency. It's blank because the RTP doesn't come with enough tiles to fill it.
EDIT: Also, don't use fucking purple text. It's annoying. I wasn't going to help you, because of it, but I decided I would help anyways.
EDIT2: And name your topics something related to the question. I don't want to see 50+ "RMVX HELP NEEDED!!11one" threads in this forum. Something like "How do I add tilesets to RMVX" or "What is TileE for in RMVX" would have done wonders.