I want to upgrade my standard mk3 front and rear speakers for direct replacement ones if I can as the sound quality has gone noticably worse recently. Does anyone know what output rating the standard ones have?

I have a Sony DJ-CA510/10 headunit and disc changer but have not upgraded anything else. The recommended speaker rating is 75W (min) and 200W (max).

Can anyone suggest some quality I should go for or if I need to change anything else to get a noticable difference in sound quality.

As you can tell from my post im not to technical so any help would be appreciated. Cheers.