Method 1

1. On your Mac, choose Apple menu  > Settings.

 

 

 2. Then click Network  in the sidebar (you may need to scroll down).

 

 

3. On the right, click on your active network name, the one for which you want to disable IPv6, then click Details.

 

 

4. Click TCP/IP. Next, click the Configure IPv6 pop-up menu and choose “Link-local only” to limit IPv6 traffic to the local network. Click OK.

 

 

 

Method 2 

Disable IPv6 entirely via the command line via Terminal. 

1. Click      in the upper-right corner of the menu bar or press Command-Space bar.

 

2. Type in 'Terminal' and double-click the item.

 

3. Execute the following command in the terminal window:

sudo networksetup -listallnetworkservices 

 

 

4. Then you will be invited to enter your Mac administrator password; please type it (your password won't be visible as you type)
and click the "Enter" button on the keyboard.

 

5. Here you will find a list of all your network interfaces and their descriptions. 
Locate the network interface you are currently using, typically Ethernet or Wi-Fi. 
Now use the following command in the terminal window to disable IPv6 on that interface: 

sudo networksetup -setv6off Ethernet
sudo networksetup -setv6off Wi-Fi

(On the example below, it is Wi-Fi.)

5. You might be asked to enter your Mac administrator password again; your IPv6 will then be deactivated.
You can double-check if it is disabled by visiting the TCP/IP tab in "Networks" as was described above: