Hi! well, for now you can't mine with GPU, as the xmrig miner has been specifically modified for uPlexa... I suppose that someone will, at some point, write a re-modified UPX-xmrig that will use GPUs, but the initial purpose of the project is to mine on ALL (or as many), existing and to come, IoT devices... So I assume that the goal is to make mining accessible to anyone. GPUs can be expensive and quite specific.

But once again, the source code has been released, so some dev will surely try to GPU-ize it in the incoming weeks.
For now, you can enjoy easy and accessible mining on your CPU!