You're outside my area of knowledge now, but the question is more clear for others to answer. As far as I can tell from a quick search, regular ubuntu has a rdp server installed and ready to enable. Not sure if U-Mate does, though.
You probably know this already, but you need a server daemon installed and running on the Raspberry Pi machine. xrdp is one common option; am sure there are others.
I also found this older post on this very forum which may be of help.