PO- PO approved partially & also paid but user want to reduce the remaining PO amount to zero

Hi expert,

Against total approved PO value of Rs. 100 user has already created GRN of Rs.40 & paid now user want to reduce this PO value to INR 40 only & not going to have GRN/paid for remaining amount of INR 60/-

what will be the solution for this. what i am thinking we can only close the approved partial PO for the remaining unused amount but can't edit further.

Regards,

Santosh