Can I free up some upload space by deleting submissions?

If I delete all the past submissions to my form, will that allow me to free up space and continue on with the free version? Question being I am getting ready to transfer the website over to  another owner and they will take control of forms, etc.

Please advise as I need to upgrade before tomorrow 12 est

Thank you

Yes, you may free up some space by deleting submissions that have associated file uploads in it. However, be mindful that this process can not be undone.

Here's a snippet from the guide I'm linking below:

When deleting submissions individually, you will see this warning message (see screenshot below). Please note that deleting submission data is irreversible and will permanently remove it in our servers, including the file uploads on them.

Complete guide: How-to-Delete-Form-Submission-Data 

So I strongly urge you to make a backup copy of your Submission Data just in case you'd still need them. There are plenty of ways to do that, feel free pick one that will work for you:

Related guides:

How-to-export-all-of-your-data-at-once

How-to-Download-Form-Submissions-as-Excel-CSV-PDF

How-to-Download-the-Submission-Files