Question about Lenovo ThinkCentre V530s

There are generally 2 slots on the V530 and V530s. Max. supported are 32Gb, but would mean that the 8Gb has to be replaced by a 16Gb ram.

Of course, you can also just buy another 8Gb Ram and plug it in, which gives you a total of 16Gb. Or you can buy only 16Gb, which results in 24Gb. All DDR4 Dimm288 min. 2666 clock or higher should work. Ram mixtures should not be a big problem today; in rare cases, however, they do occur (especially with Ram mixtures with different clocks). But you can't foresee this, or if you want to be on the safe side, make sure you buy the same Ram (open the PC, google the Ram article number and buy the same Ram).