How often should I weigh and how do I enter that new weight and change my total calorie goal?

I can't answer how often you should weigh, since it'll all come back to your personal preference.

You can enter your weight changes in "Check In". It's a subcategory of "My Home" (in the Web, I don't know about the app).

To change your calorie goal, you can change it in "Goals" subcategory, along with your macros. It's also a subcategory of "My Home". Hope this helps! ☺