Remove the slide, the. you will see a screw that holds down the laser in the frame after the screw is removed you can now remove the laser unit and change the batts. It should be on your manual.
I use a dedicated driver to remove and replace the screw. you have to be very careful torquing the screw. it is much easier with a driver rather than using the L wrench that comes with the gun. the driver I like is made by Wiha. I do not use loctite, but check the screw after every trip to the range. just be very careful tightening.