Is this a brand new fresh install? ie the very first time you have updated after install?

Have you insalled anything on it that it did not come with?

To do a screenshot on Mint Cinnamon just push the "Print Scr" button on your keyboard. That will save the screenshot in a folder called "Screenshots" in your "Pictures" folder. It will be named with the date you took it. To take a screenshot of a specific area of the screen hold shift while pressing the "Print Scr" button and you will see a dialog open where you can click and drage the area of the screen you want.

Another way to update is using the terminal.
Search in your apps for "Terminal"
type the following line into the terminal. When it asks for your password type it in and hit enter. (You will not see anything happening while typing your password for security reasons)

sudo apt update

after that command is done

sudo apt upgrade

kxmlgui5 is a library from KDE. Since Mint uses the Cinnamon desktop I'm guessing that it is having a problem updating a KDE app that you have installed somewhere. So it could be something that you will need install manually. If you can get me a screenshot so we can see what app has it as a dependancy. We can help you out more.