If you need the points from the first reservation to make the second, your only option is to cancel and rebook, and that includes whether you do it online or by phone. The risk you have if you first cancel and then try to book the new one is that you could lose both reservations between the time of cancelling one and making the other, a risk that defnitely exists at the time of year you will be attempting the change. Assuming you can find another studio open, what you might want to consider doing is the procedure created by Supersnoop, a member of these boards, that avoids the risk of losing both reservations, which is set out in my post at that the following thread
http://www.disboards.com/threads/ma...the-process-can-you-go-ahead-of-time.3461485/
On a different issue, if your intent is to switch to a studio at a near park resort (BWV, BCV, VGF, BLT, Poly or VWL) at 7 months out, you likely should not get your hopes up because it is highly likely all those will be gone before 7 months out for the time you want.