How can I remove previous owner's Apple ID?

You can't. Not without the password for the account that's signed in.

Contact whoever you got the phone from. They will have to remove that.

Go to the settings app, tap on the name of the old user on the top, and scroll down and click sign out.

Then you may as well throw it in the recycle bin. That phone is useless. Go buy a phone you can use.

There is no way to bypass the activation lock.