If your avatar has an emoji attached to it, just choose another photo as your avatar - one without the emoji. If you want to delete an emoji or photo from you chat, just long press on it and delete it.
If you want to switch keyboards, you do not have to delete your current keyboard, just select which keyboard you want as your default. You can have as many keyboards as you want and switch between them when you need/want to.
Do you mean, how do you delete your emoji of your picture that you see on your keyboard in chats? If so, go to gallery, select any photo, then edit with pencil icon, in your keyboard long press the emoji you want to delete and it should do so.
