This article covers two things, how to find duplicates in an Excel spreadsheet and how to bulk remove them.
How to find duplicate values in a column
Firstly, highlight cells you wish to check for duplicates, then:
Click Conditional Formatting
Click Highlight Cell Rules
Select Duplicate Values
How to bulk remove duplicates
Click a cell in the column you want to remove duplicates in
Click Remove Duplicates
Select the column to check, generally you'd just choose one eg: ItemCode
You will get a message saying how many were removed and how many remain.