Editing graphs in librecalc

When I moved my income earned/ day graph from Msoft excel to librecalc the accumulated
total graph seems to be a series of curved lines ( like a trend ) instead of the straight lines between points that I was used to.

How do I edit the curves to set them back to straight lines? Colours are wrong also and there are about 250 such curves and I do not want to deal with each one individually.

Please attach a sample file, reduce the size as much as possible without private information, and paste the information in Menu/Help/About LibreOffice, there is a copy icon.