This heavy duty drawer slide is from a kitchen cabinet and I can't figure out how to release it from the cupboard. I tried taking off the bottom screws, but it still won't come off. There must be a release mechanism, but I can't seem to find it.
Those appear to be IKEA drawers, there is little tab that must be pressed while pulling the drawer out. It is a little white tab, you can see it in a slot cut into the metal of the slide just a little in back of the grey plastic piece. You need to push up in it with a small screwdriver or anything small enough to fit in the slot.
A video will do better at explaining this.
Here is a video that explains the adjustment screws you see in your photos, they adjust the drawer fronts.
Turns out all you need to do is lift the drawer up when it's at full extension. It takes a bit of force. To put it back in, you just slide it in. Here's a video I found: