Hello, I own a Mexican stratocaster, 50s replica...

Hello, I own a Mexican stratocaster, 50s replica. the syncronized tremolo is balanced nicely and with the 50s style tuners it all works well. it says on the sticker on the back, set up in the factory with fender super 250s. there is no clue to what gauge they are, i want to put new strings on it, but dont want to upset the balance. Does anyone know exactly what strings to use, or is there a way of knowing by the strings thats on it now,?

If I were you I would contact Fender directly:
http://www.fender.com/support/ contact_fmic_consumer_relations.php

since it is very hard to know the answer to your question from the description you gave us