The first thing you need to do is to remove the pins holding the band in place. You will have to use a spring bar tool for this purpose. Locate the pins and position the spring bar tool at the end of the pin, keeping the spring bar tool in a proper slot. Inside the pin there is a spring which keeps the pins from collapsing. Simply apply pressure inwards with the spring bar tool in order to compress that spring.
While maintaining the inwards pressure on the pin, swing the spring bar tool and move it away from the watch. This will dislocate the pin from its mounting hole.
Remove the pin after releasing pressure on it. Follow the same technique on order to remove the other watchband pin. Remember to keep the pins in a safe place because you will need these pins to secure in place the new pair of Timex watchbands.
Both the watchbands will detach when you have removed the pins. Now it is time to get in place the new pair of Times watchbands.
You will see a slot to hold the spring-loaded pin at the end of each watchband. Place a pin in one of the watchbands and snap it back into its original location by simply reversing the procedure that you followed to remove the pins. Do the same for the other band as well to accomplish the task.