You may have to pull some trim panels to access it. They are held in by plastic pins and screws which are covered by plugs. So, be creful gentle and take your time. Work from under the dash, as is least invasive way there is no protocal for soing this, and you may have to remove the airbox that covers the air vent doors for some room.
Eventually you will be able to feel how the speaker is retained. In the end you may have to remove the trim panel around the speaker and could have gone that right from the start. But it is always best to at least have some push from behind and know where the clips and/or tabs are so you don't damamge dash.