Single tenants changing on Joint Tenancy agreements

Please see my e-mail below to the DPS. I would be grateful if you could help as when I spoke with them them seemed very vague.

Thanks

Dear Sir \ Madam,

Putting deposits in the DPS is nice and easy. However I now have a property where one individual is leaving and another moving in. How do I get a new tenants proportion of his deposit into the scheme whilst at the sametime giving the departing tenants theirs back.

If I were just to hand over the incumbents deposit to the person leaving (as your helpline told me) surely this would leave me exposed to the individual 'potentially' suggesting they did not have their deposit returned as it has not lawfully been done through the scheme nor can it be tracked through the scheme. All that would be traceable is the fact I changed the tenants names over?

I would be grateful for a swift response as this is an imminent issue