First, make sure you actually need to amend it. You can go here
Do I need to amend? to see reasons for amending.
Then, if you have already e-filed and the IRS has accepted your return, you will have to wait until they process it and you receive your refund before you can make any changes. If you try to change anything now, it will confuse the IRS and possibly delay processing of the return. If they had rejected the return, you could make changes and re-submit the return.
Finally, once the 2017 amend options is available, 2017 will become a clickable link below. You can then click it for instructions on how to amend the return.
How to amend (change or correct) a return you already filed