Hi,
You can change the folder where your images are stored by HikaShop with the "upload folder path" option of the configuration. However, that folder has to be a folder of your local web server or it won't work properly.
Now there are solutions to link a folder of your server with a third party storage server/service but it won't help for speed.
Safety is not a concern for the images.
I would simply recommend to keep it like it is by default. Sending images to clients is not a lot of load, and if you need more speed, it's better to subscribe to a CDN service which automatically serves your static content (images, CSS, JS files) for you without changing any configuration on your website.