All shared, reseller, and semi-dedicated hosting plans have a Max Request Size value of 500MB. This value cannot be modified or increased. This means you will be unable to upload any file larger than 500MB through cPanel's File Manager or a PHP based form, and would instead require using FTP or SFTP to upload the file(s):
How to upload files using FTP
How to upload files using SFTP
We recommend FTP or SFTP for uploading files as general best practice as it is faster and more reliable than any web based PHP form.