I just finished my first year of college, and I'm telling you, declaring your major really isn't important at all until you become at least a sophomore. I was originally Computer Engineering until I found out how bad I am at programming. Anyway, here goes:

You have a few options:
1) If you are leaning toward one of the majors more than the other, then declare it. You can change your major at any time, just by filling out a single form. By declaring a major, you will get an advisor with more specific knowledge about that certain major who can help you decide which classes you need to take, etc. You can still take Psychology 100 to see if you're into it, and if you find it interesting then you could always switch.
2) If you really have no clue about what you want to do, then just go Undecided. In this case, your advisor will help you decide what you want to concentrate on for the time being, and can help you sign up for classes with a variety of subjects so you can figure out what you like. At my school they also have programs designed to help undecided majors find a good major that they will enjoy.

At the beginning, just focus on taking low-level classes to see if you enjoy them and would like to pursue that major. Even if you decide to drop the major, those classes will still count as GFRs, which are classes that you must take before graduating.