Well 16x4 is 64
if you have 2 x 4 gb under the keyboard where you can't get to them that's 8 GB Total
if you put 2x 16gb that would equal 32+8 40 GB
If you put 2x 8GB that would equal 16 Gb = 8 GB would total 24 Gb
You will have to match with your new moduals the old Moduals Timmings and voltage even brand name if you can find them
You can't just drop in any old moduals they have to match what you already have.
You can get this info by using
hwinfo64
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro