How to change priority for sales order delivery in atp check ?

Hello SAP gurus,

I am facing a problem where 100 pcs in unrestricted stock and one job order of 100 pcs also one sales order for 125 pcs and STO for 75 pcs.

While doing atp check both sales order ans sto are confirming the qty. But when doing delivery for sales order first then it is picking only 25 pcs.

But we need that sales order should pick the 100 pcs from unrestricted stock. Why this is happening that stock is reserving for STO and balance is free for sales order which is only 25 pcs. How can i solve this issue ? Pls answer asap.

Thanks & Regards

Deven