You can buy bathroom switch that has already all pieces needed or you can buy different components that you will put together.
Both types of switches have plastic cover and junction box which holds whole switch in place. Only difference is that second type of switch has a frame where switches are installed in separatly. The advantages of mentioned type is that you can install filler(s)/ blanks. The mendtioned is handy when you plan to change the blank with actual switch in near future or you don't know how many appliances are you going to find in the bathroom.

In this instuctable i will use a switch that is already put together but some parts can still be disassembled. All these parts have locking mechanisms (except switches on my model) and thay can be pulled out in order to dismantle. I suggest you first check on the other side, if there's something to unlock first (screws, 'tongues' etc) before you force it.

My switches are illuminated B)

Step 1: Tools

Tools which you will need:
- Phillips screwdriver
- keystone screwdriver
- wire striper/ cutter
- drill and drill bit
- 2x bolts, 2x washers, 2x wall anchors
- screwdriver tester for 110V, 220V in Europe (optional)
- plaster and sandpaper grit size P180 or more (optional)

Step 2: Disinstall Old Switch

First determine which fuses are connected with bathroom switches. Usually one fuse is for the light only and one for boilers/ heaters. I suggest you TURN OFF all.

Next step is to unscrew and/ or pull plastic cover. Than unscrew bolts which hold whole frame to junction box. Usually mentioned bolts are in the middle of right and left edge. Than the frame should pop out or pull it with a screwdriver.

Take notes or a picture about the color and the position of wires with switches and connectors. Digital camera becomes handy here. Other method is to mark them with a pen or duck tape.

Next step is to disconnect wires from connectors. Usually connectors have bolts but there are also models which can hold the wire with cone shaped connector only (pull/ push method). .

Step 3: Prepare

First check which direction your wires are coming from. Drill or cut holes into according side of junction box (my case top) because trough mentioned holes you will put your wires. Notice sometimes the box is already marked where mentioned holes should be.
Than install junction box.

If the opening is smaller than junction box, you use a hammer and a screwdriver (or similar) in order to widen the opening. If the opening is bigger than the box, you should use plaster and let it dry before you continue.
Next step is to drill into the wall and fix junction box with wall anchors, screws and washers. You can do the mentioned only when your wires come from top, bottom or sides.

Next step is to test assamble whole switch and check that the cover is close to the wall. A groove of 3mm is quit big.

Junction box must be firmly fixed before you continue.

Step 4: Install New Switch

First you shape, cut and strip all bare ends which should be 5mm long. Usually modern connectors don't need rounded ends like you saw in previous picture.
Next step is to connect your wires like described in your notes.
Next step is to check, if all wires are firmly connected.

Now push the frame into junction box and if necessary bend your wires some more. Next step is to bolt the frame to the box and you'r almost done!

Now, with the frame secured next step is to test assemble the cover because usually there are grooves and old paint marks. You can rapair them with reparatur product, a sandpaper (grit size P180 or more) and new paint.

Assemble the cover and you'r DONE.

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