If you want the system to take the price from the last Purchase Order, then do not maintain the conditions in the info record because it has precedence over the last PO. This means that the netprice field in the info record should be left blank.
In the case when you have already maintained the conditions in the info record (or netprice), try to delete them or make them invalid by changing the validity date.
Even though no price was maintained, the info record will still keep track of the Order price history.
To check the Order price history, go into the material info record and click Environment -> Order price history
