UDM Pro Using the WAN2 port as the WAN Port

UDM Pro Using the WAN2 port as the WAN Port

If you end up using the WAN2 SFP+ port on the UDM-PRO or UDM-PRO SE, 
chances are you'll want to make the WAN2 port your primary port.

Note: These instructions are from the 1.11.0 UniFi OS Version. Newer or older versions may be slightly different.

Login to your UDM-PRO / UDM-PRO SE
Click on the Network app
On the left side, click on the Unifi Devices link
Click on your UDM-PRO / UDM-PRO SE in the main table. This will open a side-bar window to the right
In the side-bar menu click Settings
Find Ports and click the down arrow to make it expand
Scroll down to WAN Ports and click on Configure Interfaces below the two WAN port information table
Change Port 10 (WAN2) to Disable
Change Port 9 to WAN2
Change Port 10 from Disable to WAN
Click Apply at the bottom of the menu side-bar
Done!

If you click on the "Overview" link at the top of that side-bar menu, it should now show the WAN speed as 10GbE.
The only other thing to tweak from here is the ingress and egress bandwidth. 
This can be found in the Network app -> Settings -> Internet and then clicking on the WAN row of the Internet table. 
From there, click the Advanced link and scroll down to ISP Capabilities. 
Set your ISP Upload and Download speeds, save and go run your speed tests!