Before starting to unbolt things, disconnect the wiring harness underneath the playfield and label the two identical connectors with something easily identifiable. While they are still connected, you can either label them with a marker or put some kind of colored tape on both connectors of one set to ensure they get back together correctly. The wires are colored differently and you can match them up that way, but this is just another step that is recommended, making reassembly a no brainer.
Although the new switches can be installed without removing the mini playfield, it is recommended to remove it. It is relatively easy to do, just take your time and be careful.
Once everything is unbolted/disconnected, place a towel over the playfield so you can set the mini playfield down to work on getting the wiring harnesses through the hole in the main playfield. It's easiest to pull them through the hole one wiring harness at a time.
Once the mini playfield is free from the machine, unbolt all of the switches. Keep all hardware organized so you know where it goes for reassembly. Lay out the new parts to make sure you've got everything and you know where it's all supposed to go. Make sure you've got a good pen-style soldering iron and be sure to tin the pads of where the switch wiring is going to go. If you're unsure of your manual dexterity, it may be a good idea to use a third-hand tool with the clips and a magnifying glass to make it easier. Take note of the pads and look closely to which side the wires are going to go. They're also labeled on the board as to where the white and the green wires are supposed to go.
When cutting the wires from the old switches, trim them back a bit to get nice, fresh copper exposed and then tin them with some fresh solder. Do not trim the wires to length on the new switches. Leave as much wiring as possible intact for the benefit of any future repairs/choices.
As a part of the "wiring clean up" upon assembly, sheathe everything with heat shrink tubing. There is no real need to shrink it, the tubing is merely used as a protective conduit and as a way to make things look tidy.