Well, first I rake back the existing mulch a bit and edge them. Sometimes I spread the soil I generate from edging out just above the edge (which is why I raked back the mulch) and sometimes I just put it straight in a wheelbarrow and dispose of it. You generally don't want to be mixing that soil in with the existing mulch. Then I do any weeding necessary. Than I smooth the whole bed out. That way I get a nice even smooth layer of new mulch. Generally I leave any existing mulch in the beds unless the new mulch is a totally different color. Oh yeah...before any of the above I blow them out good with a leaf blower. I think that about covers it.