Merging duplicate contact entries from multiple sources
Remember: when creating a contact, you can decide where to store it. Usually, there are at least 3 choices: Google, SIM, phone.

If I read your question correctly, it looks like you have a copy in each of these places. In this case, Tirath's suggestion doesn't work, as GMail will only see what's sync'd there (and phone + SIM don't get sync'd). You then might want to take a look at apps like Contact Remover (to ease deletion of the duplicates), or Contact Remover Plus which also offers to merge or move them.