How to upload the Prestashop database to server? -

i'm working on prestashop right now. had make changes in design of prestashop website. have made changes @ database. how upload changes on server i'm not able it. please 1 tell me process?

firstly created db in phpmyadmin, made changes in prestashop & tried upload db , changes onto server gives error:

error 1045 (28000): access denied user 'username'@'localhost' (using password: yes)

by way, know how change username root , blank password in phpmyadmin.