If you are using WHM/Cpanel then in order to change that “Max: 50MiB” limit in the import section of phpmyadmin, you will have to change two values in WHM (Web Host Manager).

Step 1) Go to Tweak settings, find the “cPanel PHP Max upload size” change it according to your needs. Save changes.

Step 2) Go to Tweak settings, find the “cPanel PHP Max POST size” change it according to your needs. Save changes.

Go back to your phpMyadmin. The value should have changed.

Full details here:

http://crosstown.coolestguidesontheplanet.com/web-host/37-increase-upload-database-size-for-cpanel-and-phpmyadmin-server

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http://stackoverflow.com/questions/12707822/how-to-increase-import-size-limit-in-phpmyadmin