Yes, it's an option in the maintenance menu, accessed from the front panel. Press the round knob then turn it till you get to settings, press settings then turn again till you reach the maintenance option....
The consensus is you need a reading of around -60 which doesn't fluctuate much to do everything the B2 can do. It's important to note that lower numbers indicate better strength, so -50 is better than -60.
With my previous home wifi I was getting -61 to -63 but improved it to about 53 simply by putting the wifi dongle on a short 30cm/12" USB extension cable. Adding a new dongle with an antenna improved it again to -37. If you need to do that go for a dongle with a RT5370 chip. But note this will probably change the B2 address. There's also the option of a cable connection.