Restricting wp-admin login

This is one of those thigns that has been bothering me.  I want to limit who can access the wp-admin folder and hence the admin login script.  I’ve read about how to do it online but have had no positive results.  Apparently when Apache updated the software to 2.4 the game changed and how you use certain features that worked with 2.2 do not work with 2.4 and there’s no certain way to testing this absolutely.  What I mean is that I can try them  and then see if I can log in but because of other issues with how apache 2.2 directives may interfere with 2.4 directives causing them all to fail it is not clear which ones correct.