Okay I am going to give this a shot and someone can post and correct me (and they probably will, people on this board are REALLY good). But..as far as I know, you cannot use points AND cash for the same room for the SAME night.
So, if you want to upgrade to a 2 br....I would think you would need to use the points for the first couple of nights, then pay cash for any nights the points did not cover....
For example:
if you used 160 pts for a week in the 1 br. Then, if you switch to a 2 br, which is 22 pts/night, 54 on the weekend.....you would have enough pts for 5 weeknights, leaving 72 points. Then it would be 54 for Saturday, leaving 18, which is not enough for the second weekend night, so you would have to pay cash for that night.
Now I confused myself!! LOL But I believe you have to pay EITHER with points OR with cash for each night, you cannot book a night with a combination of pts and cash.