The size of the Magento database can increase dramatically. A lot of this space is taken up by log files. To manually flush the log files:

• Log onto your hosting via SSH
• Change diretory to your Magento store root directory
• execute php -f shell/log.php clean ( you can use --days 7 to keep 7 days of logs )
• You can check progress by executing php -f shell/log.php status
• This process can take a long time !!!