First, login to cPanel and then click on MultiPHP Editor. From the Basic Mode tab, in the drop down select the website you need to increase the file upload size on.

Change the setting upload_max_filesize to a reasonable limit, such as 100M for 100 MB. Also, change post_max_size to be slightly larger than the upload_max_filesize amount. It need not be significantly larger, but several megabytes larger. For example, you might consider 120M with a 100M upload size. Click on Apply to apply the new settings.

Keep in mind that if you change your PHP version, you may need to come back into this screen to change the PHP upload size!