Hey @Hajimuhammad!.
Welcome to the Community. I created a new post for your question. 
You can log out from Dropbox.com from the avatar or smiley face you have on the top right of your screen.
If you want to log out from the Dropbox dekstop application, please keep in mind this will unlink your account and you will not be syncing until you log back in.
You can find the steps to unlink your Dropbox here.
Get back to me with all your Dropbox questions. Thank you!
Fiona
Community Moderator @ Dropbox
https://dropbox.com/support
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