Renaming the wp-admin or something similar is not really an option due to the way WordPress is coded. However, there are ways to make it a bit harder to access.
First, you can password protect the wp-admin directory. To do so, simply follow the instructions below:
How to password protect a directory
Also, access to the login area can gained by visiting example.com/wp-login.php. This bypasses the wp-admin, so yo may want to prevent access to that file as well. Since it is located in the main area for your wordpress, password protecting that directory is not an option unless you want to password the entire site. You can, however, password protect that single file by using the .htaccess file. Below is an article on how to do that as well.
Password protecting a single file in .htaccess
Lastly, there is a wordpress plugin for protecting the wp-admin folder and the wp-login.php file. This can be found at:
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