Getting an error when trying to push changes [git]

Unfortunately I am getting an error when trying to push my commit's to my bitbucket repository:
{{

{\\ #!bash $ git push\\ Password:\\ To https://SamuelMarks@bitbucket.org/SamuelMarks/toc-and-header-footer-extraction-from-pdfs.git\\ ! [rejected] master -> master (non-fast-forward)\\ error: failed to push some refs to 'https://SamuelMarks@bitbucket.org/SamuelMarks/toc-and-header-footer-extraction-from-pdfs.git'\\ To prevent you from losing history, non-fast-forward updates were rejected\\ Merge the remote changes (e.g. 'git pull') before pushing again. See the\\ 'Note about fast-forwards' section of 'git push --help' for details. }

}}

This is a very important push, and I need it to go through.

Please tell me what I can do on my end, or if you've done what's required on yours.

Thanks,

Samuel Marks