Tom (tired of the computer)

there is a "Bump" node that basically turns a heightmap into a normal map. since you appear to already have a normal map in place, the Bump won't do anything the normal map isn't already doing. if you don't care about displacing actual geometry, you're already done (and don't need a heightmap).

if you DO want to displace actual geometry, you will use the "Displacement" node and pipe it into the "Displacement" output on the right. Then, in the Material Tab -> Settings -> Surface -> Displacement tab, choose "Displacement Only". If your mesh has enough vertices (shown below: a 6x subdivided cube), this will result in real bumps showing up on your mesh.