Take the top off with a toothpick if its a rubber one otherwise you will need to heat the carto tip in some really hot water boiling maybe to loosen the glue and force it off with a strong paper clip or a needle nose tweezer if you have some better yet here is a link how to do it 
VaporKings.com e-Cigarettes and supplies: How to refill your e-Cigarette cartomizers
but the carto should be refilled like a regular cartomizer to avoid burning it since the liquid needs to be there to prevent the burning and super hot vapor you are describing.
VaporKings.com e-Cigarettes and supplies: How to refill your e-Cigarette cartomizers
but the carto should be refilled like a regular cartomizer to avoid burning it since the liquid needs to be there to prevent the burning and super hot vapor you are describing.