Of the three ways you can change the string on a compound bow (fast-flight, single cam, and teardrop), the teardrop system is the only one which uses a bow press. A bow press will apply and hold tension on a bow's limbs, and without a press, it's virtually impossible to change the string (unless the bow is outfitted with teardrop-style string attachments that help relax it).
If you're doing this for the first time, follow all necessary measures to make sure that you and others are safe and that your equipment does not sustain damages.
Turn the limb bolts two to three times, counterclockwise. Then step on the string while you're holding the bow in one hand. Elevate the bow as you stretch the limbs.
Locate the teardrop fittings and plant the replacement string on their empty sides. Let down on the bow riser. Your strings are now strung. Ensure that the new string is well affixed all the way into the teardrop grooves.
Step with care on the new bowstring, then pull up on the bow as you flex its limbs.
Take out the old bowstring from the teardrops, then let down bow once again. The new string is affixed.
Relax the bow and press as you pull twice.
Locate the teardrop fittings and plant the replacement string on their empty sides.
Remove the old string.
Ensure that the string and cables are securely positioned against the teardrop grooves. Slowly release the bow.
Take close-up shots of your bow before you replace the string. Refer to this as your guide to correct installation and reassembly. There are different types of bow presses as there are different types of bows. However, there is only one type of bow press designed for a compound bow. You can choose from a wide array of bow strings and their matching cables. Ask your speciality store about them.
Bow manufacturers advise neophyte bowhunters against replacing their string. Instead, they highly recommend entrusting the job to a qualified dealer/ individual.