If you would like to upload files from a different Box or Dropbox account than your usual, simply log in to whichever cloud service you are using and go to your account settings page.
Dropbox: Once in “Settings,” click on the “Security” tab and scroll down to the “Apps linked” section. You’ll see the Fieldwire link(s) displayed here, and you’ll want to remove it from your account by clicking the “X” next to it on the right side of the screen.
Box: Once in “Settings,” click on the “Security” tab and look under “Login Activity.” You should see a list of all the applications you granted access to, and when you see Fieldwire, just click the “X” button to forget the app.
This way, the next time you’re on Fieldwire and try to add files from Box or Dropbox, you will be prompted to log in to either service again and can use a different Box or Dropbox account of your choosing.