ESA overpayment query

Hi - I have a client who has received notification of an ESA overpayment. He has been in receipt of the Severe Disability Premium when not eligible for it, as his DLA ended last year. The letter states:

"You were overpaid because on 04/10/16 your circumstances changed and you didn't tell the office that paid your benefits straight away that your DLA had ended and you were no longer due severe Disability Premium".

The total to pay is £1,919.15. The letter later suggests some repayment options. My query is can anybody advise on what rights he has to suggest an affordable repayment amount and plan? For instance can he offer to pay £10 per week if that is all he can reasonably afford?

Thanks in advance