Clear the gun. Remove the mag, clear the chamber. Make SURE it is unloaded.
Drop the slide, point in a safe direction and dry fire.
You are now holding the pistol in your shooting hand with a natural grip.
Use your off hand and hold the front of the slide/dustcover (the portion of the gun in front of the trigger guard). NOW, keep your shooting hand in place, but open your strong hand (keeping the web of you thumb against the tang of the frame).
Next, just rotate your strong hand 180 degrees and close it again over the back of the frame and slide.
Gently squeeze your strong hand and it will pull the slide back. It only needs to move 1mm to 3mm. While holding it here, use your off hand to pull down the takedown lever, and release your grip on the back of the slide. In the same movement, push the slide forward and it will come off easily.
I hope this makes sense and helps.