Changing rings...

[robpearson]

I'm currently riding a trek 1.2 with 50/34 fsa vero Chainset, and as a committed MTB rider I'm really struggling with spinning my legs really fast. My comfortable pedalling speed of about 70-80rpm means I struggle at higher speeds (usually pointing down hill).
My question is, can I replace my 50 with a 52 or 53 tooth chain ring? If I do, am I going to have to change the 34 up to a 39 to make up for the large gap in the ratios?

For reference, my smallest ring at the back is a 12t

Any advice gratefully accepted. (apart from references to rule 5)