Upgrade

Hi Everyone, just had a quick question that would probably be answered very easily.

I would like to upgrade the bike to have a 2x instead of the current 3x on there. I aim to ride this bike for cyclocross so im guessing a 46/36t? The bike has 8 speed STI shifters and a 12-25t cassette in the back.

Are there any supporting mods I should do before/after changing the crank?

Thanks in advance for any tips!

-Richard