Before you can do anything to your switches, you have to first get them open. there’s a couple of ways to go about this with the easiest being to use a switch opener. If you forgot to order an opener though and you don’t want to wait for one to arrive, a small flat-head screwdriver will suffice, though this will take much longer and increase the risk of damage to the casing legs.
To use an opener, simply align the legs on the top casing with the ins on the opener and the flat side with the wider face on the opener before pressing down evenly straight down until the legs unclip from the bottom casing. Then just remove the top from the bottom and you’ve got your switch open.
To use a screwdriver the same idea applies only instead of unclipping all 4 legs at once, you need to do it one by one. Wedge the screwdriver under each leg and press up and out, just enough to unclip it and no more. repeat this on all legs and the top should pop off just like it would with an opener.