You can cancel your order right up to the day of delivery and receive a refund.
After delivery, you can end your contract early. This may cause fees from the leasing company depending on how much time is left on your lease. These amounts can vary a lot so check with your leasing company.
Upgrading to another make or model is not possible mid-contract. You can end your current contract if you pay a settlement amount and then upgrade to another vehicle. The settlement amount is usually 50% of the remaining monthly payments. Settlements and arrangements will differ depending on which funder your agreement is with.
Check with your leasing company if you're struggling with payments, so they can go through options with you.