When I built my pc I bought 16gb (2x8) of ram. For the Christmas season I decided to gift myself 32gb (2x16). Both sets are ddr4 and run at 3200mt/s but are of different brands. Is it okay to put them in the other two ram slots or should I replace the old ones?
You should mix them the same way across channels. Like, put the 16s in the first slot of each channel and the 8s in the second slot of each channel. Not for compatibility reasons, but for performance. If you put both 16s in one channel and both 8s in the other, it may not perform as well, because the CPU might run them in single channel mode.