When you upload large media to your WordPress site, the upload process may be interrupted due to the size of your file (especially videos).
This is an imposed limit that can be changed.
To increase this limit you can modify the .htaccess file that is placed at the root of your site (usually in the public_html folder containing your WordPress installation).
This procedure can be accomplished by FTP or by the File Manager present on your CPanel.
This file must contain a line with the parameter you wish to modify, in this case:
php_value upload_max_filesize 512M
php_value post_max_size 128M
By default the upload_max_filesize is 512Mb and the post_max_size is 128Mb, but you can choose the value you like. If you specify a number without letters, its value will be measured in bytes. You can use the abbreviation letters (shorthand notation) for better readability: K for kilobytes, M for megabytes and G for gigabytes.