Trying to add image to here but not quite understanding this here forum.
....
Nor do I understand how I can reduce its ‘weight’ i.e it says max 3000kb (whatever that means)
Well, the size of the image is limited to three megabytes (which used to be "enormous" only a few years back but is nowadays easily exceeded by the megapixel camera images).
If your image is bigger than three megabytes you will need to downsize it with an app.
There are
many apps able to accomplish this - if you are using Windows my personal favourite is
the "original" XnView which is free for personal use. (I dislike the new XnViewMP because of its "phoning home" habbit)
As I have moved onto Linux I'm now using "phototonic" for this purpose.