1. Start in your numbers screen. Click your name in the top right corner of your screen and select "Numbers".
2. Click the "gear" icon under the Actions Menu next to your Landline.
3. This brings you to your number's settings page. You can update the extension here. (Tip - if you need to wait any amount of time between entering extensions, you can use a "w" for every 0.5 seconds to wait. ex. If when you call your landline, you have to press 1 in the first menu, and then 2 seconds later you need to enter the number 2 in the next menu to reach you directly, enter in your landline as 1wwww2. This tells us to wait 2 seconds before entering the extension)
4. Click Save in the bottom right corner.