Haw can change calories

If you have WatchOS7 then;

How to Change Your Move, Stand, and Exercise Goals

To change your Apple Watch activity goals,press the digital Crown and open the Activity app in the main menu.

Apple Watch menu

With the app open,scroll down to the bottom and tap on "change goals".

You can now adjust each goal in order, starting with your Move goal. Use the Digital Crown or on-screen buttons to adjust the value to your liking. Tap “Next” and you’ll be able to adjust your Exercise goal in 15-minute increments. Tap “Next” one more time to adjust your Stand goal, in hour increments then tap "ok" to finish.

For watchOS6;

Tap on the activity app on the watch and scroll down to the bottom;

On your watch open the activity app

Hard press on it then tap the plus or minus sign then tap update

https://9to5mac.com/2020/06/19/apple-watch-how-to-change-exercise-goal/