how to remove icloud lock without owner

Activation lock can be removed only by the following methods, as described in How to remove Activation Lock

• Entering the Apple ID and the password with which it was set up.
• The previous owner removing the device from their list of devices at www.iCloud.com/find.
• Start an Activation Lock support request which requires proof of purchase - a sales receipt.

Edit - FoxFifth has added a method for a family member's device, this too will be successful if the deceased person was a family member, which you have not mentioned.

See instructions in How to request access to a deceased family member's Apple account - Apple Support