It's hard to tell from that angle, but there could be a tab on the side of the plugs that you need to release.
I have taken your photo and pointed out where I'm talking about.
If there is a tab it's often obvious by looking at it that the tab needs to be pushed in for it to release.
Sometimes there is just a alignment pin too that goes into a extra hole in the board so you can only plug it in one way and not get them mixed up.
If you don't see any tab on the side of that plug that you can push in then it simply maybe that hard to pull off. I do run into that once in awhile.
If you want take another photo of the plug from the side I will take a second look.