Component(gearing) upgrade question
In terms of the rear derailleur, you will need to determine the capacity you need.  

To do that, add together the teeth in largest rear cluster and largest chainwheel to get the max teeth you have.  Then add together the small rear cog and the smallest chainwheel to get the min teeth you have.  Subtract the min from the max.  That is your capacity needed.  

You can then go on to the Shimano site and gets the specs for the derailleur you are interested in to see if it has enough capacity.  You will also need an 11 speed chain cut to fit.