I cannot print my 2017 tax forms because i began my 2018 taxes but decided not to file, how do I delete them so I can download previous forms for school enrollment

You don't have to delete anything to print your 2017 return.    Starting a 2018 return does not prevent one from downloading a 2017 return.    However, if the 2017 return was prepared in Free Edition and access is locked,  you'll need to upgrade to PLUS and pay 19.99 by credit/debit card to unlock it.    And that involves paying for the 2018 return, even if you don't actually prepare and file a 2018 return.  We can tell you how.

Have you located the online 2017 return, and is it in the SAME account as what you started for 2018?   And when you try to download the PDF, does it say access is locked and that you have to pay first?   If so, what you need to do is upgrade the 2018 Free Edition return to PLUS, then pay 19.99 by credit/debit card.   We can tell you all the steps.

Is the return you started still in Free Edition, or did you already upgrade it to PLUS?   I will be including the steps to upgrade it and pay.

There's also a free option if a return transcript will suit your purpose.   You may be able to immediately download one at the IRS website if you qualify to open an IRS account there.  Otherwise, to order a transcript to come by postal mail takes 5-10 calendar days.
http://www.irs.gov/Individuals/Get-Transcript