I have found that many species of Hebe, if left, produce most of their green growth at the top and you are left with bare stems. They need to be lightly trimmed on a regular basis. They do not respond to heavy pruning. Having said, some of the larger species like Midsummer Beauty will stand hacking back and will come again with a vengeance. So you can give it a go and knock it back low down to anything that looks like a possible bud.

I did hard prune one some years ago (nothing like as tall as that though) by cutting back half one year and the rest the next. It resonded very well.

welcome to GoY :o)
I've renovated a hebe by removing 1/3 down to 1ft and the next year another 1/3 and the 3rd year the remaining 1/3. it then was easy to keep it in check with flowers every year.

when removing 1/3 I removed them evenly around the bush so it didn't look lopsided.

do you know which variety you have?