It looks like you've been able to update the images in that area, but the images are the wrong shape (so they're being stretched). The ideal dimensions for these images are:
You can first resize the image to the largest dimension, then crop the image to get the correct width and height in an image editor on your end. Keeping the dimensions small like that also makes the file size of each image smaller meaning they'll download faster.
If you'd like us to put together some image slides for you and upload them there, we offer this as a service for $50 +GST. In that case, you just need to send us through enough images to make about 10 slides and we'll do the rest. Let me know if you'd like to do that instead.
RE uploading images to other areas of the site. We have an Image Gallery module that you can add to your site (choose Image Gallery from the Add a New... menu). Within that you can create categories, then within those, upload images. We're doing a bit of work soon to update the look and feel of the Image Gallery but you can still get started now and that'll be updated for you automatically.
You can also just insert single images into pages in the site as it looks like you're already doing :)
Please do let me know if you need any more help.
Have a great weekend! :)