It looks like Wix is asking you to change the nameservers for your site -- this will change over DNS, which will likely result in the MX record, which currently points inbound emails to your domain name (fitsquiz.com) to Sonic, either disappearing or changing to a default that Wix provides. You may only need to change the 'A' record if you are just moving the hosting of your website over to Wix. (They have a guide here
on how to just point the website at Wix.)
If you plan to move both DNS and web hosting over to Wix, you can change the nameservers via the following menu in Member Tools:
Web Sites / Domain Names --> Domain Names --> Domain Name Tools --> Modify Authoritative Nameservers
You'll need to click 'Modify' next to your domain name, click 'Unlock' if necessary. Next, un-check the existing sonic items, enter in the values provided by Wix, then click Update Nameservers, followed by 'Lock'. It may take a few minutes for the changes to take effect, but that will switch over DNS to Wix.
-- Joe M.
Sonic System Operations