Your location flag is showing as the United States.... you might want to alter that in your profile.

You can cut them back, but taking them down very low when they're mature can be risky, so if you really don't want to lose it, best do it in stages, taking say a third this year, then more next year. If you're prepared to risk losing it, cut it back as much as you like during May, and wait to see if it recovers, because it might - give it a good feed after you've done it with something like Growmore raked in at the base, and maybe top off with some composted manure or good garden compost. If it doesn't recover, you can always plant something else.

Agree with the above,as I do the same with mine when needed..they come back well,if you follow the advice given...