Use this guide to upgrade the RAM in your 2017 model 21.5-inch iMac up to a maximum of 32GB (16GB x2).
Tools
iMac Mid-2017 21.5" RAM upgrade Guide (iMac18,1 / iMac18,2)
Use this guide to upgrade the RAM in your 2017 model 21.5-inch iMac up to a maximum of 32GB (16GB x2).