Using and modifying modules

I’m a noob. Now that’s out of the way, I am going to be running The Sunless Citadel for a group of five.  I’m thinking I may want to up the challenge a bit in some encounters. Is it possible to increase the HP on stat blocks for any of the monsters?  Can I add more monsters to encounter areas in a premade module? thanks! Chris

Yes and yes. Once you have installed a module or addon, you can modify it to your heart's content. It's as if you spent the hours and hours needed to make it yourself.

Thank you!  Now...  How exactly do I do that...?

If you want to edit a monster's base stats game-wide, open their entry in the journal tab (not the Compendium tab), click the edit gear icon and enter new values. If you just want to change the hit points of any deployed monster, click on the token on the map, and enter e new value in the appropriate bubble. If you want to increase the number of monsters, use copy and paste on the tokens, or drag out additional tokens from the Journal Tab or the Compendium Tab.

Awesome!   Thanks!