Hi Claire,
Weirdly, the Bank of England hasn’t released a date yet! They’ve got to give six months’ notice of when it’ll happen, though, so we’ll know about it. Also, if you have any paper notes left after that date, or already have old paper fivers hanging around, the Bank of England still has to honour them and change for new ones. In fact, you can still take old £1 notes to the BoE and get them exchanged into today’s money!