I just replaced my 32gb of oem ram that I bought my system with like 2 weeks following purchase.
I picked up the 64gb kit of hyper x fury ram.
Yes the logic with buying 64gb on top of my already purchased 32gb was ridiculous, but I too found out that you couldn't mix. It worked out well though as my hyper x fury ram ended up having issues and had to be sent out to be exchanged. Luckily I had my 32gb oem ram to use while I waited!
The stuff you replace it with...will no doubt be better anyway. The heatsinks on real aftermarket ram are quite necessary, and the fact that the Dell oem stuff doesn't have it... is kind of cringey.