Cara - Without knowing which watch you purchased, I cannot be specific. But the bracelets for most modern watches -- the genuine model & most better reps -- have several links that are held together with small screws. So all you need to 'size' your new rep is to unscrew 2 screws to remove each link. Often, there are 4-6 removable links per bracelet, which allows for a wide range of possible sizes. After you remove the link or links to fit the bracelet to your wrist, simply reattach the remaining links with the screws. As long as you can use a small screwdriver & you are careful not to scratch any of the polished metal surfaces around the screws, the process is really quite simple.
Good luck & welcome.