Upgrade Wordpress CiviCRM Version from 4.5.2 to 4.6.5
I had a similar issue upgrading from 4.5.8 to 4.6.4, what worked for me was to manually remove the civicrm_mailing_abtest table from the database. 
Restore your database backup before the upgrade and login to mysql

Update:
To restore your backup database:

mysql -u root -p // login to mysql

drop database civicrm; // delete the current database, the one is failing to upgrade

create database civicrm; // create a new empty database

quit // logout from mysql


Restoring the database backup

mysql -u root -p -h localhost civicrm &lt; /path/to/your/database/backup/civicrm-database-backup.sql // write the backup to the new empty database


Replace "/path/to/your/database/backup" with your backup directory and "civicrm-database-backup.sql" with the name of your Civicrm backup SQL file.

Check for the existing civicrm_mailing_abtest table

mysql -u root -p

use civicrm; // replace civicrm with the name of your database

show tables; // it will give you a list with the civicrm database tables


If the civicrm_mailing_abtest is listed in the output, remove it, as it shouldn't be there, the A/B Test mailing was introduced in CiviCRM 4.6

drop table civicrm_mailing_abtest; // this will remove the table


After that proceed with the upgrade again.

Hope this helps

Update 2:
If you have permission errors after the restore, you will need to grant permission to the civicrm mysql user

mysql -u root -p

grant all on civicrm.* to 'username' identified by 'password';

flush privileges;