You can access and change the files in your wordpress install via FTP.
You will need to download an FTP application such as Filezilla (link to download) to connect to your Wordpress install using your FTP credentials.
You can find your FTP Credentials via the PHP FTP Details button in the control panel menu.
You will need to enter the Host, Username and Password credentials as found on this page.
Example of each below.
Once connected you will have access to your local folder directory and also the remote directory where the wordpress install can be found.
Generally this can be found in the public_html folder.