Installing 2 x 16GB of OWC RAM

Hello,

Could someone please advise me about installing 2 x 16GB of RAM I bought from OWC. I have a 2020, 27 inch, 3.3GHz, i5 iMac, with 2 x 4GB of RAM inside. My question is do I remove the 8GB of RAM my iMac came with & install the 2 x 16GB MODULES? Or do I leave the 2 x 4GB MODULES in the iMac, which would give me 40GB of RAM? When I install the RAM, what slots do I put them in? Starting at the Bottom of the iMac slot up the way towards the top of the screen. I do not know if the slots have numbers on them.

Thank you to anyone who can help me install this RAM The proper way.