Slide a new roof jack sized to fit your vent pipe over the pipe.
Replacing a roof jack.
Place your ladder securely against the roof eave and climb up on the roof.
The first step to replacing a damaged roof jack is to measure the size of the existing roof jack to make sure you purchase the correct size.
Is it necessary to replace roof flashings when replacing shingles.
Find the damaged jack and take measurements of its height and pipe diameter.
On the boots if you have metal roof jacks with rubber boot seals on top with many models the rubber seals can be popped off and replaced without removing the metal part and there are also slip over boots that can just nestle down over the existing damaged boot and overlap the top of the jack but contractor would have to look at it and see then go get parts so if using a contractor probably cheaper to just have him bring new ones right off unless quite close to his supply wholesaler.
Remove any roofing nails and slide out the shingles.
Installing new shingles is a major investment for most homeowners so it makes good sense to take steps to protect the integrity.