Use the search button to find all the topics related. I'm sure there must be numerous threads on here.
To get access to the back of the unit, You will need to remove the plastic side panels ( marked red circles ). These are 4 pieces. Start with the lower two by removing them near the gear knob. Use a butter knife, the clips are quite sturdy so you wont break anything. Once the lower two panels are removed, remove the top two as well. Next, unclip the air vents by pulling them towards yourself. Its held by two push clips so use your putty knife. Put it to the side after disconnecting the hazard light switch. Finally the unit is held by 4 8mm bolts. remove those to pull out the unit and have a look at the back.