I have a Mac OS Sierra.
I have a 2011 Mac macOS Sierra 10.12.6. Can I update it any more? Please send me an Update if possible or what do I need to do? thank you!
iMac 21.5″, macOS 10.12
You can upgrade it to High Sierra but not beyond that. See the following from Identify your iMac model - Apple Support
iMac (21.5-inch, Mid 2011)
Model Identifier: iMac12,1
Part Number: MC309xx/A, MC812xx/A
Latest compatible operating system: macOS High Sierra 10.13.6
See instructions in: How to download macOS - Apple Support
You should also use the current version of a 3rd party browser such as Chrome or Firefox since you will not be able to use the current version of Safari with High Sierra.