you'll have enough play in the dropouts for a 2 tooth difference... depending on where your axle is now.
if you go up 2 teeth, the axle will move forward in the dropout.

you don't need any tools to install the freewheel. you can use your chain as the tool. search rotofix or rotafix.
http://204.73.203.34/fisso/eng/schpignone.htm
you'll need a tool to take it off, if you need to in the future.