The first things to check (or ask your host provider to check) are the values of upload_max_filesize, memory_limit and post_max_size in the php.ini configuration file. All of these three settings limit the maximum size of data that can be submitted and handled by PHP. One user also said that post_max_size and memory_limit need to be larger than upload_max_filesize. There exist several workarounds if your upload is too big or your hosting provider is unwilling to change the settings

FAQ - Frequently Asked Questions -- phpMyAdmin 4.1-dev documentation