How to disconnect hard drive?

A couple of months ago I replaced my iMac 2010's optical drive with an SSD which it now boots from (Sierra) and holds all the software. Most of my files and data are on the hard drive but this has been backed up to Time Machine. I did this because the hard drive was starting to fail. Which it has now done. How do I disconnect the hard drive completely as it is clicking away and the fan is going haywire?