Also a potential confusion is size can mean two different things to both computer software and the humans using it:
1. How physically large a pic appears on screen
2. How much memory the file consumes
If you have a mac and iPhoto I can help you.
If not someone else who knows what your software names the two things above must help you.
Here's how to control size if you have a mac and iPhoto:
In iPhoto, with the pic open go go File, Export...
Kind: PNG (this is a format which is not compressed, like JPG is, so it may appear more clear.)
Size: CUSTOM Max dimension 800 px (this is my preference you may prefer larger or smaller or want to spec horiz or vert size)
Then click "EXPORT"
Name the file and tell it where you want the system to place it.
Also our screens are larger horizontally than vertically so when possible (as in your first two pics) rotate the pics so they are horizontal not vertical.
What a lovely collection - my favourites are the pear pink spinel & Osiris gems's amethyst in 'liquid flower' design (& well done for coming up with such a lovely name ).