Upgrading memory

I have a Pen-mmx 166MHz computer which I would like to replace memory on or add memory too.
I know it has 4 72pin slots empty now, and 2 128pin slots with one filled with a 32mb DIMM
how do I find out what memory to purchase ? I’d like to stick with the 128pin DIMM option. I do not have any documentation on the board. I can see when booting the following:
Bios v4.51pg
when I pause as it is showing me the memory count I can see the following number at the bottom of the screen: 12-11-97-i430TX-2A591Dac-00

any suggestions how to go about getting the right memory for this computer ?