This is not a P30 but is a P2000 which is functionally similar. The main difference being that with the P30/SK I believe the slide lock lever is captive where in the P2000/USP etc. it comes completely out.
Step one is to grasp the frame and slide and retract it slightly to the cutout in the frame as shown by the red circle. (obviously remove magazine, clear the weapon etc. first).
I find using my right hand oriented as shown gives me plenty of leverage to slide and hold the slide back in proper position especially with the hammer back.
Once you have the slide and notch lined up properly with the slide lock lever you use your other hand to push the center of the other side out and it should push fairly easily out the other side. You will need to use your third hand to take pictures of the process.
Again on your P30 I believe it is captive and will not come completely out where as on the P2000/USP series it will come out.
Once you have pushed out the slide lock as shown (removed on the P2000/USP, just pushed out and left captive on the P30 then you will be able to slide the slide assembly right off the frame.
Hope this helps.
Chris