Launch A New App And Remove The Calling App From Any Open Processes?

I am writing an updater for our application and having an issue overwriting the files. Here is a long drawn out example. Test.exe is our main app and update.exe is our updater application. Test.exe needs to launch update.exe and then close test.exe. Update.exe will download the new updates from our website to a temp directory and then copy in the new updates. The problem I have is when Test.exe has an update and I try to copy in the new file it says it can't because test.exe is still in use. I "believe" this happens because test.exe is still running in the appdomain because update.exe was launched from test.exe before I closed that app.