Hi Alec, there is a replacement guide for the LCD screen on a Garmin GPS [[Topic:Garmin Nuvi 2589LMT|here]].
In reference to your question, sometimes there is extra adhesive on the LCD screen. You should use a metal spudger, from the [product|IF145-072|Ifixit Pro Tech Toolkit], to gently pry underneath the sides of the screen until it separates from the device. Be careful not to tear any of the wiring or components of the device.
Let me know if this does not work!