Pretty straightforward -
1. Note the orientation of the spring that returns the peg if it folds up. (have a beer)
2. Take a standard (flat) screwdriver and slide the c-clip out of the groove that holds it. (have a beer)
3. Slide the hollow, cylindrical bolt out of the bracket and peg. The peg and the spring should be free to remove. (have a beer - you're doing great!)
4. This is the only difficult part, you may want to have a beer and take a few deep breaths. You need to hold the bracket, the new peg and the spring, all in their proper orientation in relation to each other as you slide the hollow, cylindrical bolt back through the whole assembly, ensuring that the return spring is in the proper orientation that you noted in step 1. If this step is successful, have two beers but DON"T let go of the assembly yet. (I told you this would get tricky)
5. Slide the c-clip back onto the groove of the hollow, cylindrical bolt. If you can do this, the task is complete and you should have a complete bracket/peg/spring assembly. Congratulations! Have a shot of tequila and six beers but DON'T DRIVE!
Good luck.