The error gives you a suggestion that may be correct, the mirror(s) in question could be in the middle of a sync causing them to be temporary unusable.
You could try:
sudo apt-get cleansudo apt-get updatesudo apt-get upgrade*** from command line ***
Or wait a few days and see if the issue resolves itself.
If you want to adjust the mirrors, you could edit:
/etc/apt/sources.listand/or an appropriate file from the directory:
/etc/apt/sources.list.d/*** Once you’ve edited any of the files be sure to run the former commands so that changes are reflected ***
If any of these steps scare you, you can also hire me for an hour to address the issues for you.
*** Professional, Affordable, Trusted Technical Assistance – tpnAssist.com ***