Upgrade instructions are located in the documentation folder of the downloaded code.
For 6.01 which is extremely old to upgrade its real easy. Unzip the downloaded code delete the data and uploads directories as well as both config files and the install file. Upload everything else. Run the upgrade.php script in your browser and select the 6.0 upgrade all the way through to the last one for 7.0. You then delete the upgrade script off your server.