Login to the device by typing http://192.168.1.1 int your browser.
Enable Remote Management
Head to Administration and Remote Management.
Select Yes next to Allow Secure HTTP Management. Make sure the radial button next to Everyone is selected.
Protip #1: If you haven't done so already, make sure you change the default administrator password for the router
*Protip #2: Make sure to change the default port, from 443, to something else as 443 is primarily used for SSL.
Create Users for Administrative Access
Click Add under Add Users to create an additional administrative profile. Be sure to fill out the information and set a strong enough password.
Click Apply to save changes.
Enable admin policy
Under Login Policies for the user you created above, uncheck Deny Login from WAN interface and click Apply.
Your users can no login to the router from the WAN side by typing https://wanIPAddress:Port# (replacing with the correct info) and logging in with their newly minted username/password.