If your account is hosted on a shared server then you will not have SSH access to server but you can ask for private SSH like jaileshell which will allow limited access of your account.
Once you get SSH access you can execute following command :
chmod 755 foldername -R
where foldername is the name of folder to which you want to assign permissions.
Note : Its not recommended to assign full permissions as its a security risk and anyone can upload/execute malicious content to your web site.
If you have a dedicated server then you are free to connect it and assign the permissions.
Regards,
ST
Professional UK Web Hosting
Last edited: May 25, 2011