The IRS does allow you to set up an installment plan if you are unable to pay your balance in full by April 18, 2017.
You should pay as much of the balance due as possible before April 18 to reduce underpayment penalties and interest (which will begin to accrue on any unpaid balance after that date). You can then apply for an installment agreement if there is a balance still owed.
You can get more information and apply online for an installment plan at https://www.irs.gov/individuals/payment-plans-installment-agreements. Please note that there are fees involved in doing this, in addition to any penalties and interest that may be assessed.