If you wish to increase the upload limit for phpMyAdmin in plesk, you need to change the upload limit in php.ini of psa.
It can be done from the below steps.
1. Open the following file.
vi /usr/local/psa/admin/conf/php.ini2. Change the following. (Say 80MB)
upload_max_filesize = 80M
post_max_size = 80M
Now save and quit..