Sorry but the software is designed to protect and if you choose to disable it then it will warn you. You might as well not use it if you are going to run your machine with it turned off.
Perhaps if you gave more details as to why you want it turned off plus what operating system and service pack this is we might be able to offer some help.
I am using Windows 7.
The product is not turned off. What if I only want nightly scans? Real time scanning is a resource hog. Why keep real scanning files that were scanned the night before?
That's Windows 7 SP1 I trust, if not it isn't supported and there's help with that here: https://community.mcafee.com/docs/DOC-2205
Real-time scanning is the full-time scanner that actively protects your machine and should only be turned off in exceptional circumstances... so you meant the actual scan itself.
You can stop scheduled scans and even stop automatic updates if you want although in the case of the latter at least have SecurityCenter warn you when one is available. They come in at least once a day.
However, on my machine at least, updates are so silent I don't even know they are happening unless I spot the activity on the taskbar icon. I don't see a performance drain.
Sometimes a major update will ask for a reboot, do so as soon as you can.
For those settings:
Double-click the taskbar icon to open SecurityCenter
Dismiss any blurb that may be apparent at the top
Click Virus and Spyware Protection
Click Scheduled Scanning
Alter the schedule there to what you want.
Real-time scanning can also be altered there but I don't recommend turning it off, except in rare instances, for instance if you were installing a major system update such as a service pack.
As I said, turning it off will elicit frequent warnings.
To change the way it updates click Updates on you main screen and then Settings.
Again don't turn that off though, unless you want more alerts.
There are also some general settings for alerts in Navigation (top right) > General Settings and Alerts.