Depends what operating system you're using but it's most commonly flushed during reboots. If you're using Windoze you can use the ipconfig command in a console window.
Start > Run then type cmd and hit Enter.
In console type ipconfig /flushdns and hit Enter
Are you sure it's a DNS issue? Are you the only one who cannot view the site?
Maximum Cash Discount on any plan with MAXCASH