Dear Murali,
Scrap value depend on following cases;
Mukthar reply is good if we have maintain cutoff key in depreciation key then changes from dep key.
other wise we can manully changes scrap % in asset master and run AFAR
please mention your cases,you want to decrease scrap value then i will provide you proper solution.
if useful life of asset is complete then only scarp value will show in asset then access amount will transfer in Retained Earning account