Absolutely! If you're a current Mags Member and want to upgrade to Mags+, just select the Mags+ Membership option as if you're purchasing it for the first time. When you reach the payment stage, the system will automatically recognise your existing Mags Membership and apply a £39 discount - so you'll only need to pay the additional £10 to upgrade.
It's a quick and easy way to unlock all the extra benefits of Mags+ without paying the full price again.