If you would like to upgrade to W7 Phone Developer Beta or simply uninstall it you cant do it through Add/Remove Programs in Control Panel.
You need to go the location path of it:
C:\Program Files (x86)\Microsoft Visual Studio 10.0\Microsoft Visual Studio 2010 Express for Windows Phone CTP – ENU
something like that :p
then right click on the vs_setup.msi file and select Uninstall,and it will uninstall the W7 Phone Developer CTP.
Now you can install W7 Phone Developer Beta :)