Disk Utility tells me that I need to "reformat disk" before it is restored?

[iMore Question]

My desktop iMac (mid 2010) has been crazy slow. I ran Disk Utility, and the resulting message was I needed to 1) back up, 2) reformat disk, and 3) restore backed up files

I have used Time Machine for back up -- your site was very thorough and helpful!
but am uncertain about how to reformat.. any help??

Thanks!!

 

[Just_Me_D]

The information from Apple via the following link should be helpful to you.

https://support.apple.com/en-us/HT201376