You may want to use a heat gun or hair dryer to heat up the adhesive holding the screen to the rest of the display assembly. These adhesive strips are located approximately 2 cm away from left and right edges of the screen and 3 cm from the top. This video shows where these strips are located.

Alternatively, using the iOpener may heat up the adhesive enough to remove the screen from the rest of the display. Please visit the iOpener Instructions guide for more details on properly heating the iOpener.