There is no limitation set for the maximum file size which you can upload with cPanel's File Manager. However, it is not recommended to upload large files through it because the transfer may consume a lot of system resources and end up corrupt the file.
Our cPanel is equipped with the CloudLinux to avoid a single account slowing down other accounts on the server to ensure the server stability.
Instead, you are strongly advised to use FTP for bigger file transfers. You can use an FTP client that suits you best - FileZilla, CuteFTP, SmartFTP, etc.