I would like to be able to reduce the actual size of some images on my site as they take too much room.
In the Content section template I do not see this option (nort do I anywhere else actually...)
Can you please advise as to how I can achieve this? I have tried uploading small images that just end up being stretch to fit the canvas...
Image sizes are determined by the template/theme your are using and there is no way for you to change what that is as GoCentral doesn't offer access to the code to make those tweaks.
Maybe look at another theme that has the image layout and sizes your prefer?