tweeter replacement help

[NIKOSLAR]

Hello,everyone in here.My intetion is to replace my speaker's tweeters with some better ones.The problem is that I don't know much about what is the old tweeter specifications, 1'' or 1,8'' and so on.and what type of tweeter do I have to put in order to have the perfect fit and much.
I will have audible difference?
I appreciate your possible help.Thank you.
Regards Nikos.Greece.
You can check the picture I have uploaded.

 

[DUG]

Get more information on what you have.

There is more to a speaker than just size.

Model #
impedance
crossover frequency

Carefully remove existing tweeter and look for information on the back or edge of it.
(four outside screws)