was given iphone 6s by my friend and he doesnt remeber icloud password he used to open the account and i want to remove that account on the phone and use mine

Removing Activation Lock requires either knowledge of the Apple ID and password or the original proof of purchase (POP) to remove.

You could use iforgot.apple.com to reset the iCloud password associated with the iPhone 6s.

Without the Apple ID and password, using the original POP requires a contacting Apple Support so that the POP can be validated (matching serial number, IMEI, purchase date, and/or name on the receipt) and then Activation Lock removed. Once removed Apple Support can walk you through restoring the iPhone so you can associate it with your account.

Your friend can reset his account's password via http://iforgot.apple.com