If it's Leycesteria, you can pretty much do it anywhen. You haven't given a location, but it's probably fully hardy where you live, certainly on the south coast for me it's been more semi-evergreen than deciduous, and tough as old boots.
If you cut it down now, keep in mind that flowering next year will be affected:-
The current stems which are left will sprout side-shoots, these will flower in early summer next year, while at the same time there will be strong new upright growth from the base which will flower later in the summer.
So you can cut to almost ground level to control the plant and get one big flush of flowering next year, or cut some or all stems to a higher point, to get a more diffuse effect.
You will probably find that it seeds everywhere, and sends out runners too. So you can divide it if you've got a special variety but I've never bothered, in fact you can have too much of a good thing.

I wasn't aware this plant COULD be divided - the RHS suggests hardwood cuttings or from seed, doesn't mention division, but the BBC site says 'divide in spring' - not clear whether they mean the seedlings you've grown, or the actual shrub.