I want to copy a form from last year and use it this year. I edited the form but I want to remove the 2017 submissions.

First, you might want to download all the submissions data, as Excel or CSV, for that form in order to back it up. https://www.jotform.com/help/73-How-to-Download-Form-Submissions-as-Excel-CSV-PDF 

Then, you can filter submissions and delete the ones from 2017 through the submissions page:

https://www.jotform.com/help/377-How-to-Delete-Form-Submission-Data 

Let us know if you need more help, we will be glad to assist you.