There are engineering disciplines that focus primarily on concrete things (civil engineering), others that focus primarily on abstract concepts (software engineering, process engineering). Still others combine the two realms to some degree (electrical engineering). Then there's the problem domain: computers, software, roads, chemicals, bio-systems, etc.).
Spend your first year in engineering school learning the basics - all engineering disciplines follow a similar underlying process. Try to decide on the problem domain you'd most like to work in: what turns you on and energizes you? If you decide to be a software engineer and really hate computers and software you probably won't be happy in your career.
And realize that the skills you will learn may be transferable - that means if you're an electrical engineer for a few years and decide to switch to biomed, you'll need to get more education but the problem solving skills you've learned will be transferable to the biomedical field.
Make sure you hone your writing and other communication skills in college - too many engineers come out of engineering school barely able to write a coherent sentence. And employers increasingly do value communication skills in their employees. It's the sort of thing that will really help you stand out from the crowd!