Hope this helps:
Here's a good video tutorial: https://www.youtube.com/watch?v=HiujAReaNRk
You will need to remove the bad caulk with a screw driver or you can buy a device to scrape it out. Then clean the area and let dry over night. Make sure it is good and dry. Then apply new caulk.
Use a butter knife it works great get the end started and pull