Depending on the account holder's credit, the account's payment history, and other things, you may be offered to upgrade early by doing a DPP. (monthly installment payments). You'll probably not be eligible for an early upgrade if you're a year or less in your current two year agreement, or have made multiple late payments/been suspended for nonpayment. You'll be notified by email and/or a notification in your MyVerizon Account if you're eligible. The only other options is to pay the ETF for your line to end the contract and then process your upgrade. hope this helped.
Buy the 6 full price, sell the 5S on swappa, glyde or similar service. unless you are offered early trade in and DPP, this will be next cheapest option - if you want new. Consider a used 6 for cost savings also.
You can't pay off the ETF and be allowed to upgrade to a new phone.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.