If you would like to upgrade to a later version of the theme then WordPress expects you to delete the existing one and then install the new version in the same way as a first time installation. So if you have made any changes you might want to make copies of them first.
In order to delete the theme you should go to Appearance and then Themes in the admin menu. You need to activate one of the other themes by moving your cursor over them and selecting the Activate button that appears. You can then move over the Scouting Challenge theme and select Theme Details. This brings up a menu with a Delete link in the bottom right which will take you through the process.
You may then install the new version of the Scouting Challenge theme in the same way as a first time install.
It used to be the case that if you were using a child theme you could simply remove the parent and it would automatically be deactivated. However from WordPress version 4.0 things are different. You have to activate a theme other than your child theme or the Scouting Challenge theme in order to remove the latter. Once you have removed the Scouting Challenge theme your child theme is no longer shown as available. When you install the Scouting Challenge theme again your child theme will show up and can then be activated.
If you are using the Easy Theme Options plugin it is worth opening up the theme options and saving them again, just in case any new options have been added. This will prevent PHP warning messages being generated. If you have things configured so that the PHP warning messages appear on screen this becomes particularly important.