I had this issue as well! I am also using rpg maker vx ace. You need to manually look through the files and find a file that says "RPG makers". There, you select rpg maker vx ace (wip) and there will be all the available walls. floors, and decors! You have to move the files you want to use (for example, B-C-D-E_Bathroom_01) into the "Tileset" file that is in the file with the name of your project. Graphics go in the graphics, audio into audio and etc. I hope this helps! :D