Slow speed white updating only

I am using zorin os 12 from last year. Everything works fine and smoothly.
But from yesterday, I get very slow internet speed in the terminal. My Problem is:

Whenever I try

Code:

sudo apt-get update

or

Code:

sudo apt-get upgrade

my speed comes while downloading the updates goes to 4 to 5 KBps while I am using 1Mbps internet connection. However, my browsing and other downloading works fine . The problem comes only in the terminal updating and upgradation command.
I also tried to change the best to the best location Still have no effect. Also did a edit in nsswitch.config file according to one answer found on web.

Thank You.

OK, that second command is wrong - by using 'upgrade' instead of 'dist-upgrade' you are effectively telling Zorin OS to update to Ubuntu which will lead to a broken system. 'dist-upgrade' does not mean updating the distribution, it is a command to tell the current OS and apps to update any package updates to match newer kernels that are installed. As for your source, don't just look for a different one in your locality, change it to 'Main Server'.