Most brush changing is extremely simple.
Undo the cap on the outside, and look. The brush is held in with a metal spring, and usually the wire has an eye for a screw connection. Sometimes its soldered, but thats all there is. carefully lever up the spring, insert the new brush. Do what is needed to swap over the wires. put the cap back. job done.

 

Looking at the parts diagram it appears you need to remove the top cap and maybe another part or two. Bosch 1618 Parts List and Diagram - (0601618039) : eReplacementParts.com part number 816 is the brush assembly.

 

your '18 router has the same motor as the 1617....
the brushes are under the black plastic caps that are located on opposing sides of the upper motor housing...
remove the caps...
remove the old brushes...
reassemble...

 

Dont forget to make sure the thing is unplugged. . . .

Im not saying you would do that but there are people out there who would. They might find it shocking!!!>>>

 

There is always a spring involved. Be prepared to hang onto it, or it might fly to the most impossible to find place. In routers with screw on side caps covering the brushes, the caps are what usually become airborne. It's a relatively simple job to change brushes, if you don't loose something in the process.

Charley