Double click the room, click on the settings tab(there should be like, 6 tabs), there should be 2 boxes there, for width and height. Just type in whatever you want.
If you need more space -x or -y, use the move all objects button in the objects tab.
I'm going to second the recommendation to get studio. Convince whoever you have to, it's only 1$ on Humble Bundle right now and will make everything much easier.