If its noiseless pups you want then these babies are the ones. Great pups and it does exactly what it says on the tin "noiseless" (if you have it earthed correctly).
In terms of upgrading then if its a good squier then it might be worth the investment but these pups are more expencive than the guitar so as previously said keep the old ones or you will lose nearly 100% of your investment.
Buy Fender SCN Noiseless Strat Pickup Set online at Musician's Friend