To change some user settings on the web app do the following:
1.) Click on the person icon on the top right corner of the screen.
2.) Select Settings
3.) Make the desired selections. Make sure to click on the Save button when done.
For the technically inclined: all times are stored as UTC times (Greenwich time) in the devices. Making the correct time zone selection here assures that the web app graphs display the correct time the events occured.