Please help with edits to score

I need to make three edits to a piece I have just written out for my leaving certificate, for example change the key , tempo, dynamics etc. I know how to change the key but im not sure how to change the dynamics and where do I have to put them on the score ? And can I go from p to mf or are there specific rules? Also I dont know how to make a change to the tempo and where to put it on the score ( at the start , end ? ) if anyone can help me in anyway i would greatly appreciate it I have an exam in a few days !! Thank you