Formal:
* Je montrerai (This is the most common and formal way to say it.)
Informal:
* Je vais montrer (This is more casual and translates literally to "I am going to show.")
* Je montrerai (The formal version can also be used in informal settings, but it might sound slightly stiff.)
It's best to use the formal version "Je montrerai" unless you are speaking to someone you know well and are using informal language.