Rename one of them to something you will recognise
Upload this by FTP and verify it appears on the /static/xxxxxx URL as described above
Now please log in to http://YOUR-TEST-SITE/ with the username provided - this user will have access to 'site admin'
Go to the Dependencies option on the 'site content' menu
This list of dependencies is how you add CSS and Javascript files to the document header. Click 'add new' to add a new dependency - note the different types you can add, and the ability to easily enable and disable them.
Fill in the 'filename' box with the name of your uploaded file (eg. default2.css ), then choose either of the CSS types under 'Type', and click Save
View the source of http://YOUR-TEST-SITE/ again to verify that your newly uploaded stylesheet is included in the header, in place of the default.
Make a small change or two to your CSS file and upload it again
Verify that your updated file appears after doing a full refresh (CTRL+F5)
Using your QuickOrder Developer username and password, check you can log in to the developer forum at http://forum.quickorder.uk.com/ - you can ask general questions and request features there, but in some cases you may be referred to the main support desk.