How can I clear my underarms?

Hello, I have razor and shaving but now, I have to dance school and raise his arms wide, but I'm sad because my underarms are very dark (and will dance with a partner on the side) so I would like to know if someone tells me as cleared in 2 weeks, and which method is right for me to shave without obscuring my skin, lasting longer and not irritated, Really I need it...!!!!