Place the fabric right side up (that would be the right side of the fabric, the one that was facing your serger foot). Even if you can't remember, it's easy to recognize. Just look for the side where the two straight seams are obvious as opposed to the wrong side where the right seam comes out as spots that keep the loops together rather than a line of stitches.
Place the sharp tip of the seam ripper in between the loops, where they form a V.
Pass the seam ripper under the straight seams (left and right needle stitches). If you're using a 3 thread overlocker instead of a 4-thread overlock, you'll only have one of those.
I found it that it's easier for me to pick up both seams with my seam ripper but harder if I cut them at the same time. So I just pull both out but cut only the left stitch.
Then grab one of these ends of the left stitch and pull as much as it will let you, until the seam thread breaks.
You might get lucky and manage to pull the entire line of stitches.
Repeat for the second, right needle stitch.
It should look like this with both removed. If the seams break before you're done unpicking the entire seam, repeat the steps above.
Then simply remove the upper and lower loop stitches. At this point they should come off right away, with no effort since they have no support left (which was offered by the left and right needle stitches).