Hi Orlanda,
I assume that you are entering the Credit memo in Adagio OrderEntry, and choosing to return the item from there? Where are you looking to to determine the quantity of the item stock?
When OrderEntry credit notes are posted with the choice to Return items, the quantity on hand is immediately updated everywhere except the costing lots (whether LIFO/FIFO or not). The quantity there is updated when Day End processing is performed, and also the cost is updated here too.
The process seems to be working fine when I try it. Before posting a credit memo, use the Item Inquiry function and the Quantities screen, which shows the qty on hand at each location. Then after posting, go back to this same screen and compare the results. If nothing has changed, then either 0 quantity was selected on the credit memo, the 'return' checkbox was not selected, or there are possible errors in your data. Make sure that a data integrity check is performed.