A toggle clasp consists of two components--a ring and a pin--that attach to opposite ends of a bracelet to close it around your wrist. An extender for a toggle clasp allows you to enlarge the bracelet. The extender is a series of links with a toggle clasp pin on one end. They can be found at beading and jewellery-making supply stores and come in different sizes and metal types so you can match the extender with the toggle clasp on your bracelet.
Lay your bracelet on a flat surface.
Take the pin end of the toggle clasp extender and insert it into the ring end of the bracelet toggle clasp.
Place the bracelet on your wrist and insert the pin from the toggle clasp on the bracelet into the round link on the extender at the desired length.
Use wire nippers or needle-nose pliers to remove extra links from the end of the extender if you don't like the extra links dangling on your wrist.
This method also will work for extending necklaces with toggle clasps.