How do I control the humidity in my frogs tank?

[Camden]

Hi there, new frog owner here, you've probably seen me around as this website is my main source of information.
I'm going to petco tomorrow (Don't worry, I didn't buy my frog there, he was bought at an actual reptile store)
and I'm going to pick up some stuff, a humidity gauge, temperature gauge, and a new lighting fixture if they have a good one.

and it got me thinking, if the humidity is too low or high in his tank, how would I lower it? (I dont think it being too high will be a problem.)

Also, if I do get a lighting fixture I'd like to have one with a dimmer or at least a timer. What kind of bulb should I get?

Thank you!

- Camden