Your User details can be updated in the user profile on the Web Portal if you are an admin or Portal User (field agents can only access the App), you can go to the profile icon > my profile > make changes and save.

If you have the user permission  to do so, and would like to update and change another users details from the Web Portal, you can go to Users > View Users > Edit (on the user whose details you would like to update) > Update the User's details > Save.