@ruchin78 You cannot import PO, Invoice and BOM items from V4 to V5, because table structure is changed. In V4 you BOM items will be in column AE4, like wise in V5 it in CD4. You can verify this by importing the BOM from V4 and V5 and compare it. V5 has twice the number of columns and some of columns.
If the BOM is too big, then you copy the raw materials from V4 excel to V5 manually and upload it back. That is probably only solution I can foresee for you.