Assuming you mean Yucca gloriosa, unless you want to dig the whole plant up, the best thing to do is wait till the babies have roots, then sever from the parent and pot up or plant out individually.

thanks for your reply.i really dont know what it is but its about 16ft tall the top looks like its had it but cant reach to do anything to it. how do i know if the babies have roots?i pulled one off mum and stuck it in compost will that do it ?

Usually what happens is the babies arrive, then over time, they start to put down roots and then grow on, developing their own root system as time goes by. Wait and see what happens with the one you've separated, but like any baby, it spends a while taking nutrients from mum till its ready to go alone...