if you are in limp mode then you'll have to do a service regen. for this you will need a decent scan tool as mentioned above. EfiLive, Tech 2, etc. or take it to the dealership.
if you remove it and clean it, the ECM wont know that the ash load has been reduced or a cleaning has been done so it will remain in limp mode. you will still need a way to clear the codes and get it to start a regen process