(Before making the following changes, make sure to have a current backup of your files and your database.)
You're going to do three steps: A) edit the configure.php settings and upload them, B) rename the admin folder, C) test login to the new folder.
Details are below:
There is no need to alter the admin configure.php in v1.5.x when renaming your admin folder. Simply proceed to step B.
Using your FTP software or your webhost's File Manager, find your Zen Cart /admin/ directory. Rename the directory to match the settings you just made in step A.
NOTE: DO NOT advertise this new foldername, else you defeat the entire purpose of renaming it. And DO NOT EVER put it in your robots.txt file!
To login to your admin system you will now have to visit a new URL that matches the new name used in steps A and B above.
For example instead of visiting www.example.com/admin/ visit www.example.com/NeW-NamE4u/
Without applying extra efforts to your connection on the internet you are wandering around an unsecured environment. Before you make administrative modifications to secure Zen Cart® and its database, you need to equip yourself with secure ways to make these modifications. Otherwise if someone is watching/listing to the information you transmit, it might not be long before your private business information becomes public. The bare minimum you should have is access to shared SSL services from your hosting company.
The preferred would be to have a dedicated SSL certificate for your store, as it is more professional in appearance than the use of a shared certificate. There will be ...