First of all, if it is under warranty send it to URC. That is the only way to ensure there is no damage to the remote.

The twisting method I have always seen worked great for the 700, 800, 850 but the 900 is a totally different animal and I never tried it on that one.

Remove the batteries first and the back cover.
I usually use a plastic screwdriver from my last MRF install (The little ones that come with the MRF for setting the ID). The 900 is fairly tricky to open without damage. If you look from the back of the remote where the light grey trim meets the dark grey/black back of the remote near the USB jack you can see where the two plastic pieces meet. Insert the plastic screwdriver in that seam (DO NOT PRY ON THE USB PORT) and start separating it there, the back will actually lift out of the face. There are a lot of little plastic tabs holding it together. Usually using two plastic screwdrivers allows you to keep it from snapping back together. You must carefully work your way around it to release all the tabs.

Did I mention? If it is under warranty send it to URC for repair.