Most schools will list how undecided works. Generally your large or midsize publics or even LACs are set up for this. Typically though one will end up in a liberal art or science which cover most your majors. Some majors, like public health or business or limited enrollment majors like Poli Sci at Maryland, , may not be accessible or have pre-reqs including a gpa or may not offer the curriculum you desire…some public health require a lot of science.
You might find that once you pick a major you are behind a semester or year. Just depends on what you pick, # of credits required, what you came in with ap wise and how your gen ed line up. Or you may end up just fine.
Most kids change majors and schools are typically set up for this, especially in the liberal arts and sciences.
If you need some thoughts on specific schools let us know. But most will have an undeclared section on their website which will give you direction.
Good luck.