I am a bloody idiot, but I found the option now and resized the window, but I can't get it back up with any mouse press or key (I accidentally made the window too small ;;) and reset options does not work with this either.
You should be able to enlarge the resolution with the left click! But if for some reason you can't, you can always close the game, delete the settings file (delete the file config.sav located in C:\Users\(NAME)\AppData\Local\PocketCrystalLeague), and launch the game again! That should fix it.
