The admem program isn't going to help. the 512K you see, is all there is, IF your A1000 has the ram card added to the front panel.
You will have to add more RAM chips to add anything. There were several boards that would add RAM internally, but they are almost impossible to find these days. It would be a bit more than just soldering chips in - you have to make a Printed circuit board. This really isn't out of the question, IF you have the artwork for one. Radio Shack used to sell PCB kits!
The Starboard RAM expansion (those horrible external boxes) actually work quite well. I use one on my old A1000 for RAM and SCSI.
Good luck....