Quite often RV builders use one of the many standard sizes of car speakers for their built-in speakers. If you measure the size, you can get any of a myriad of replacements from the usual car audio shops, usually most any of which would be an upgrade. If it's in a cabinet, you may need to get access to the back to measure things. If they're in a ceiling, they probably pull down (held up with spring clamps of some sort) or have screws holding the speaker grills up.
On Coachmen RVs of a certain vintage (that apparently included mine), there was a tendency eventually for the factory speakers to come loose inside the cabinet and fall down due to the heads of the screws they used not being large enough to adequately grip the speaker frame. A speaker sitting on the bottom of the cabinet sounds predictably muffled and bad. I know you don't have a Coachmen RV, but perhaps you're suffering from some similar problem.
If you're talking about speakers built into a television set or sound bar, as opposed to ones mounted in the RV, it will likely be very hard to get a suitable upgrade.