Upload the entire semisecure-login-reimagined/ directory to the /wp-content/plugins/ directory
Activate the plugin through the 'Plugins' menu in WordPress
Optionally, navigate to the settings page to re-generate the RSA keypair (a keypair will automatically be generated when you first activate the plugin), choose a secret-key algorithm, uninstall the plugin, or check to see if there were any errors
If upgrading manually, make sure to disable and then re-enable the plugin (upgrading through the admin interface will do this automatically)
For best results, make sure your blog's character encoding is set to UTF-8
If using a caching plugin, it's a good idea to clear the cache anytime you upgrade or change the plugin's settings