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I'm sorry, I'm quite confused on what you would like to do. If you would like to allow your users to upload files on the form, then you can do that by following this guide: https://www.jotform.com/help/332-How-to-Create-Upload-Forms.
If you want to change the max file size limit, you can do that by checking this guide: https://www.jotform.com/help/33-Changing-the-upload-size-limit
You can also enable the "Allow Multiple" option in your file upload field:
With that option, your users can easily remove the previously selected file in the upload field:
I hope that helps.