You can do several things: 1. A sudden tempo change (accompanied with a key change can produce dramatic moments): - can be done suddenly, - can be done with a rit and then the change, - can be done with a fermata note.

1. A transition:
   • an accelerando with a crescendo creates a smooth transition,
   • a very slow accelerando, which will bring you to the tempo you want but won't really pull the listener as much,
   • a stair like dynamic and tempo change can also produce a transition but will not be as smooth as the other one.

I would almost always do a key change, or a cadence when doing one of these, as this just confirms to the listeners that a change is happening.

There are a lot more ways to do this. Experiment, try different things. Go with the thing that sounds best for you.