what you need to do: just go to the homepage www.powdertoy.co.uk then click on download version 53.3 (NOT BETA) then save it somewhere in downloads (best to make a new folder like powdertoy) and save it in there, after doing that you press the right mouse button on the file (should be called powder-53.3-win32) then press extract to get the powder.exe out of it and you can play by clicking the application simple isn't it?
Please use a more specific thread title in future. Please make sure you provide information such as your operating system and TPT versions so we can help you more.
Download TPT and Extract the EXE using the right click menu and Extract Here. Copy the extracted file(s) to the same folder as your old TPT file and overwrite.