
This video shows the procedure of the RAM upgrade: Here are some RAM modules that should work:

Your iMac 27" supports up to 32 GB RAM (4 x 8 GB RAM modules). You need RAM that matches the following specification: The programs you use are using a fairly high amount of RAM, having the maximum capacity your iMac supports will ensure that it stays viable for years to come, and that the programs you use will enjoy the optimal performance it can deliver.
