Latex/bibtex: how can I change the template for in-text references from IEEE brackets format to else-harvard to parentheses?

Question

I just downloaded this template https://www.overleaf.com/latex/templates/eth-zurich-disco-thesis-template/hkkbptgjgyyr and want to adjust it to my needs. All works fine, except changing the references. I want them not "bla bla bla, [2]" but "bla bla bla (author, year)". Usually, if I want to achieve the latter I use

\bibliographystyle{elsarticle-harv} 
 \bibliography{references}

and all works fine. Not so in the disco template. First, I thought I could just change the main file (thesis.tex) from

\bibliographystyle{IEEEtran}
\bibliography{references}

to my code above. Well that only kinda worked. I had the "Biblabel" in the bibliography. I solved that commenting out the following three lines:

 %   \@mkboth{\textsc{\bibname}}{\textsc{\bibname}}%
    %   \list{\@biblabel{\@arabic\c@enumiv}}%
    %       {\settowidth\labelwidth{\@biblabel{#1}}%

So the label in square brackets disappeared from the bibliography. But what on earth would I need to change in the discothesis.cls in order to make the in-line references from square brackets to parentheses?

Thank you so much!