Image gallery and changing colors

I use simple php gallery https://relativelyabsolute.com/spg/ , Just upload the folder and upload your pics, very simple to use. It took me about 5 minutes to theme it into my site . https://www.scottdot.org/gallery might be somthing you could look into if you want a simple gallery.

yo, though i cant figure out how to upload that on my site, how can i change the picture at the top of the web page? like when i delete the pic file that is displayed it goes blank but no pic takes its place then i put it back and its there again. could someone please explain what i got to do? im useing Filezilla