These you can cut down to the base completely. It would regrow a whole new top. All that brown stuff is dead and will never grow again.

If this has been outside all winter it may in fact be totally dead. They are not fully hardy in the UK.
But do as Bathgate says, cut it down to the sil level and see if it regrows.

Thanks for that there is green shoots on them so not quite dead yet!! Stay safe now

If you are in a place which might get frost I would wait until the frost season is over before cutting the dead growth away especially since it is not fully hardy in the UK. If it is hard to get rid of that dead material later which is acting as a blanket at the moment then ignore it and hope it gives additional support to the stems later. If the dead stuff appeals to the nest building birds they might help themselves to it. When it dies down in the autumn you can cut it back and put straw over it, if you cannot take it in to shelter.