Open your .htaccess file and add Rewrite Rules:
RewriteRule ^myregister/?$ /wp-login.php?action=register [QSA,L]
RewriteRule ^mylogin/?$ /wp-login.php [QSA,L]
If your wordpress installed in a subdirectory:
RewriteRule ^myregister/?$ /subdirectory/wp-login.php?action=register [QSA,L]
RewriteRule ^mylogin/?$ /subdirectory/wp-login.php [QSA,L]