Unscrewing Ancient P-Trap

Ayuh,..... With a pipe wrench, 'n cheater handle if necessary, loosen the nut lookin' piece on the right in this picture,........

For the trap, it appears to be a collar to the left, put yer pipe wrench on that, 'n turn it off,.....
That should allow ya to pull the trap, 'n the chrome dress collar off the pipe goin' into the wall,....

I'm not very confident with the terminology, so i labeled the photos with what I think you folks are referring to.

So first I loosen "A. the slip nut", and then what? Does the trap unscrew from the collar?

Thanks,
Andy

I actually just redid the measurements on everything and I may be in luck and can perhaps use the existing JTrap as is. It measures 8 1/2" to the center of the existing drain pipe that drops down from the sink, AND the new sink also has a drain that's 8 1/2" to the center of the drain. I think that means that (like in the video) I can just unscrew the nut, pull out the existing sink and plop the new one onto the existing Jtrap.

I guess I freaked out because I'm afraid of plumbing! Also, the existing sink is old and its drain is 7 1/2" from back to middle, so there's a 1" gap between the sink and the wall. I guess 7 1/2" was the standard back in 1960?

Also - I guess I should clear out the JTrap. Is there a risk that if I try to loosen the clearout cap that the whole thing snaps? It seems pretty sturdy.

I know that it would be recommended to replace all the piping but that would be too big a job for me and I would tackle it with a professional when we eventually redo the bathroom - rip down the tiles and "plaster on chicken wire" walls behind that. I've attached a photo of what is inside the wall. Photo is from the adjacent room which we redid a few years ago. Luckily i have a photo of what to expect.