How to upgrade my node with bitcoin wallet GUI from 0.11.2 to 0.12.1? Install qt V5.5?

Question

i want update my RaspNode (rPi 2 B+) to the 0.12.1 but i want to use Bitcoin wallet GUI. So, it's necessary to install QT V 5.5...
V 0.11.2 use QT 4.8, but 0.12.1 uses QT V 5.5

How to install QT V 5.5 for raspberry ??