Item level and header level release strategy for purchase requistions

Dear All,

Background: We have a release strategy defined for purchase requisitions (PR) that requires releases to done at 3 different levels (by 3 different users). Item level release (implicitly) has been set in Document type and Release Group. Users at all 3 levels are able to release purchase requisitions at item level.

Question: We would like to change this to item level release at level 1 and overall release (Header) for users at levels 2 and 3. How can this be achieved with changes in configuration?

Please advise.

Thank you.