contact syncing issues between mac and ios, and what about removing duplicates?

Hello all my friends:
i need to make some big edits in my contact linst, removing some friends remove duplicates, etc.
am trying using my mac to do so, and am selecting the same account, the Icloud account,
but some edits that i made did not apply to my Iphone contacts, for unknown reason,
also, the app is very slow and unresponsive on mac, is there a reason for that?
also, i tried removing duplicates, and the app always crash,
if so, how can i remove duplicates from Iphone?i got an app called Contact sync, it is very accessible, but can not remove duplicates also,
sorry many questions, but i need to decrease unwanted contactsThanks for your help.