If you have duplicate contacts, you can merge them, two at a time.
Steps
Select My Apps in the top menu
Go to the Contacts App
Select More Options and choose the Merge Contacts option
You arrive on the Merge Contacts page.
Select Start Merging Contacts
You arrive on the New Merge page
The merge process allows you to choose a contact whose details will be prioritised if there are any conflicts between fields, i.e. two contacts with information in the same field.
On the left select the contact to prioritise, i.e. keep
On the right select the contact whose details will be copied across to the contact on the left - unless there is a conflict
Press the Save button
The merge takes place in the background