How hard is it to switch majors at UIUC? Can I take up Maths or stats major along with the major i was admitted for?
Depends on the major, check the department’s website. I believe Math and Stats are both relatively easy to transfer into.
As for double majors, it’s a little tricky due to colleges. If you’re in LAS you can double major in Math or Stats. If you’re in a different college, you can get a “dual degree,” which if I recall is a bit more involved than a double major.
I do not know the major to which you were admitted. Double majors as most think about them are somewhat more complex at UIUC than other universities and rules vary among the UIUC colleges as to whether you can do so at all, or whether you must instead seek a dual degree program. If you were admitted to a major in the Arts & Sciences college, then you can potentially seek a dual major in math or statistics unless the major you are in has significant overlap with math or statistics, e.g., if you are in molecular and cellular biology you likely cannot seek a dual major in math or possibly statistics because your existing major already includes many math courses. Moreover, you cannot declare to do a dual major now, need approval of your academic advisor, and usually need to wait and make the request for beginning of junior year.
If your current major is not in the Arts & Sciences college, then your only option will be to seek a dual degree program. That is something usually not sought until for beginning of junior year, requires approval of the applicable department (Math) in the Arts & Sciences college, and automatically adds 30 hours (essentially another year) to the total hours needed to graduate, e.g., if your current major requires 120 hours to graduate, you will need 150 for a dula degree.