Dude both places are far away from each other...if you want to reach kasol..ist you can have taxi or bus from delhi( kashmiri gate bus stand)...10-15 km before reaching kullu ..their is a place name as Bhuntar...from bhunter their are many taxis and buses to kasol...
if you are going to Bir you have to travel palampur from kull by local bus or taxi..nd from their Bir is almost 75 km