How to switch phone numbers between lines and cancel a line?

[rdraft5]

Goal: To cancel Line 2 and use Line 2's phone number on Line 1.

Ex.
Line 1: Unlimited Data - Upgrade Date 2017
Line 2: 2gb/month - Eligible for Upgrade now

So can I just cancel Line 2 and then switch Line 1's phone number to Line 2's old number?
I want to do this without paying any crazy fees.