I actually have both installed in LMDE. I need WICD when I do updates because it will connect when you drop out of X, where Network Manager will not. When I am in my normal usage mode, I disconnect WICD and use Network Manager, which works better for me on the desktop. The reason I don't use WICD for both is that one of my apps will not connect through WICD for some reason.
Bottom line is that I learned the hard way about doing my updates outside
of X so that my video doesn't get borked.
Getting back to your question, just left-click on the WICD icon and it will bring up your connections. You can then disconnect, and let Network Manager handle your connection. It will also work the other way around.