How to use an app?

Since you have downloaded an app, remember that you have to turn off its automatic updates because theyit will use the internet. If you don’t have a package, your bill will be much bigger.will be higher.

While much bigger can be said, it does not sound natural. I suggest using what I put in the green highlight.

Very good! On a side note, if you are addressing a singular object (an app), you cannot use (they)