Hi,

Generally it is best to cut out one feed per week (or if you feel you need to do it more quickly, 1 feed every 3 days or so) and replace with formula. This gives your body the chance to gradually downregulate and stop making milk. Right now you are probably in full milk making mode - to stop abruptly will put you at risk of mastitis. Stopping gradually also allows you to assess more fully how your baby copes as more formula is introduced to his diet. Be aware, also, that the amount of formula on the side of the can is quite large - this may mean your baby goes longer between feeds, and you may find that your breasts become uncomfortably full. If they are, express a little off to keep them comfortable and prevent engorgement.
I wonder, have you sought medical advice about this? It is easy to think that breastfeeding + "hormones all over the place" (It isn't clear what your symptoms are) = stop breastfeeding and all will be back to normal. That isn't always the case, and breastfeeding is important - and shouldn't be sacrificed if it won't fix the problem anyway.