Latex reference order

When I compile the latex file, I find that the references are not listed in the order of their appearance. I am not sure whether this is because there are citations in the figure caption, and change the bib style to ieee trans does not work.

According to here, this could be addressed by adding the following to the preamble.tex

\bibliographystyle{unsrtnat}
\usepackage[numbers,sort&compress]{natbib}