hi
with colorbox, you have 2 main options for slideshow.
slideshow : If true, adds an automatic slideshow to a content group / gallery (default value: false).
slideshowAuto : If true, the slideshow will automatically start to play (default value: true).
1- if you don't want a slideshow, set slideshow option to false. then you always have to manually change picture.
2- if you want a slideshow with a manual start, add slideshowAuto option to false. then the slideshow doesn't start automatically and you have to manually start it.
to do that, you have to edit inc_header.php, line 218 (colorbox config).
1-
slideshow: false,
2-
slideshow: true,
slideshowAuto: false,