Overwrite data of ontology

[kumar rohit]

I want to save item price entered by users in file. Samsung Galaxy hasPrice
?value.
User enter some value and it is stored in the file. After some time,
another price for same Samsung Galaxy is entered and it is stored. But the
problem is that the old price is also there.
How can I overwrite the previous values with recently entered value so that
my ontology save and shows one value at a time.