Use the stick until it's gone. Just be sure you are clean when you apply it. You should only need to apply it once a day. Whenever you are getting ready is a good time. When you shower wash your armpits.
Its very important to change your deoderant. When using deodorant you should always makesure you are clean first. When your underarms aren't clean the smell and bacteria and sweat clings to the deodorant stick and IT WILL NEVER LEAVE. So there is no set time to change your deodorant sometimes it is needed to be changed before the stick runs out because if there is a0bacteria then the whole purpose of deodorant is useless because it will no longer do its job. Find a deodorant that works for you and try not to switch brands too much.
DISCLAIMER: The messages on this forum and any links to external websites posted within the forum express the views of the respective authors. They do not necessarily represent the views of the administrators or moderators. Any advice posted here is for support purposes only. It is not intended as a substitute for advice by a qualified health professional.