Begin by mixing one large beverage of choice, my choice today is a very large 7 and 7.
Unplugging the unit, never work inside of a unit with the power hooked up.
Remove the 2 philips screws on each side of the unit. Carefully remove the cover.
Place all small parts in a dish or something so you will not drop them or somehow lose them.

There are two philips screws that hold the meter lamps in place and 2 philips screws that hold the dial and indicator lamps in place. You do not need to remove them, loosen them enough to be able to slide the housings back gently to gain access to the lamps.

The fuse lamps are 8v 200ma lamps, if one is bad it is advisable to replace them all. The indicator lamps are 8v 40ma pin type lamps that will require soldering to install them.

They will solder in from behind.

The meter lamps are also 8v 200 ma and should also be replaced with the dial lamps.
Replace the lamp holders after installing the new lamps, be sure to tighten the 4 screws.
I like to clean the inside of the face plate while I am doing this, dust and such does get behind the face plate and your unit will look much nicer if you take the time to clean this.

Remove the knobs and slide buton by firmly pulling them off. I usually soak these while I am removing the face plate. Remove the 4 5/16 bolts and soak these also.

Remove the brass retaining ring and the face plate is free to remove and clean. Be careful not to leave any streaks or lint while cleaning the face plate.
While in here there is marginal access to the pots and some switches, you can do some good here but there are better vantage points for switch and pot cleaning.

Carefully clean the inside of the dial area before reassembly.
Without smudging the glass reassemble the face plate in reverse of taking it apart.
Replace the cover, plug in the unit and check your handy work.

Here is a great source for lamps.
Replacement lamp GuruJim