My claims starts with something like: "Claim 0.1" How do I change the numbering? Maybe to something like "Claim 1".

• you are not giving any information but presumably you are doing something like use \section without using \chapter so the solution would be to use a class without chapters, or use \chapter as your top level sectioning command. – David Carlisle Nov 7 '15 at 15:55
• Welcome to TeX.SE! Your question doesn't give us anything like the information we need to help you. Please prepare a minimal working example (meta.tex.stackexchange.com/questions/228/…) to help us help you. – dgoodmaniii Nov 7 '15 at 15:57
• Is Claim a theorem-like structure? – Bernard Nov 7 '15 at 15:58
• Is this what you're looking for: tex.stackexchange.com/questions/104098/… – API Nov 7 '15 at 16:07
• Presumably you've added the Theorems Numbered by Section module (if you're using the standard article class) or Theorems numbered by Chapter (if you're using a book or report class). Hence, deleting that module will likely help. (You must have added some modules anyway, as Claim is not available by default.) – Torbjørn T. Nov 7 '15 at 16:07

The Claim environment forms part of a "Theorems" module. It can be numbered in a variety of ways. Most likely you have it set to be "Numbered by Chapter" (or perhaps "Numbered by Section"):