I shall tell you how then!
Go to the admin area, then click on the manage members button, there should be a list of options on the left side of your screen, click the members button then in the panel on the right there should be a bunch of drop down menus, there is one saying join request, go into the drop down menu in that and click whatever option you feel happy with!
Hope that helps! ;D
Also if you need any help with running the group, i'd be more than happy to help! I am a huge Sonic fan and run several blogs about them!