You could, but it will require custom coding to change how it loads the items. The portfolio is actually a blog post which is why it’s loading them by date. The other alternative is to create a manual based portfolio in a page instead of using the blog category + post method. You also have the option of using a plugin like this: http://wordpress.org/plugins/my-posts-order/
There might be other plugins that do this as well so best to check them out before deciding.
First, no need to say sorry if you are new to all this, even I’ve been at this for over 3 years and it’s still ongoing, especially when WordPress makes changes.
Anyway, depends on what you want to do….I would recommend trying the plugin method first. Did you try that option yet?