how i can remove the icloud account from iphone 6s i parchase it second hand

If you don't have the account name and password you can't remove the lock screen.

Take it back to where you bought it.

That is the Activation Lock which is an anti-thief software from Apple hence there is no way to defeat it.

You honestly can't bypass it without knowing the previous owner's password. You either need the account and password to which it is locked, or the owner to whom it is locked needs to remotely remove the lock via the Find My iPhone function of iCloud.com.

Here are steps you can take a look at, but you will defienitely need to contact the owner some how. You should never purchase a phone anywhere if you are not able to keep contact with previous owner or be sure they have removed the device from their account. Your best and only option really is to find out how to contact the previous owner some how.

What if I purchase a device that is still linked to the previous owner's account?

Contact the previous owner as soon as possible and ask them to erase the device and remove it from their account. For complete instructions, read how to remove a device from a previous owner's account.

http://support.apple.com/kb/HT5818

The previous owner can follow the steps below to remove the iPhone from their account:

If the device has already been erased

If the previous owner is not present

Contact them and ask them to follow these steps to remove the device from their account:

1. Sign in to their iCloud account at www.icloud.com/find.
2. Choose the device from their Find My iPhone device list by clicking All Devices and selecting the correct device.
3. Click "Remove from Account" to remove the device from the account.