It's not easy as the front of the centre console has to come out, but it isn't impossible. just needs time and patience. This comes up a lot and the best guide I know is here link. But you only need to got to step 8 and then the gauge unit can be removed. The bulbs are those small 1.2W capless types (might be type 286)
As for the speedo ... this is easier. One screw holds the bezel in the dash. Remove that and you can get to the three screws that hold the speedo in place. There are two electrical connector blocks on the back which you might have to pull out BUT MAKE SURE THE IGNITION IS OFF when you do. Sorry to "shout" but all the lighting electrics go through the dials and pulling the plugs while live will damage something. If you are really concerned about this, disconnect the battery -ve terminal -- but make sure you have any radio codes to hand first.
HIS: 1998 156 2.0 TSpark with Sport Pack 2, sunroof and hi-level spoiler in Alfa Rosso. V6 intake mod, clear side repeaters and Zeatek undertray.
HERS: 2009 MiTo 1.4 95bhp Turismo arrived 21st November in Techno Grey with colour-coded headlight surrounds.