Wedge an opening tool between the case of the watch, and the glass screen bezel.

Pry the screen bezel away from the device.

If you have a difficult time getting the front bezel to separate from the case, try warming the watch up with a hair dryer.

There are three very tiny springs that are compressed between holes in the case and the front bezel. They can pop out once the bezel is removed, so don't lose them! Remove them and put them somewhere safe once the bezel is removed.