I had a similar problem. I cut half of it right back one year. It sprouted again from low down so the next year I did the other half. Not promising this will work for yours but it did for mine. Yours is too big to try moving so it depends on how much of a hurry you are whether to try my method or get rid and start again.

It's passed it's sell by date, you can either cut it hard back to near ground level, some hebes will respond but can be painfully slow, some will just give up, another option is to cut very hard back but leave one of the lower bushy branches, this you can carefully bend to near the middle of the plant, dig a slight hollow through the fibrous root system, then peg the branch into position and mound up around the bushy growth, leaving a few inches of growth sticking out, after one year this will all of re rooted, you can then cut the branch away and grub out the old crown, refresh with decent soil/compost and move the new propagated hebe into position, I have been successful many times over the years adopting this process.