phpMyAdmin allows by default a maximum upload size of 8Mb for importing a sql file.This can be sometimes too small.
The maximum import size is stored in the php.ini file located in the PHP directory. Look for the line named upload_max_filesize and change it accordingly:
upload_max_filesize = 128M
However, sometimes the server has also a maximum execution time which should be increased to allow a larger upload.
For considerably larger imports, the command line should be used.