This document help you in restore of backup file, where the backup files size is more than 300 MB
Note - 'post_max_size integer' sets max size of post data allowed. This setting also affects file upload. To upload large files, this value must be larger than upload_max_filesize. Generally speaking, memory_limit should be larger than post_max_size. When an integer is used, the value is measured in bytes.
However, Allow unlimited post size by setting
post_max_size to 0.
By default the PHP has the limitation of uploading file size which is limited to Max 256 MB
If you have the backup of more the 256 MB and when your try to upload as shown below