I first arrived the US in 2010 using J1 visa but I didn't have income that year. Started at 2011, I filed the 1040NR-EZ since I was considered as a nonresident alien. For the tax of 2012, HR from the school told me that it's my 3rd year in the US and I'm a resident for tax purpose. So I filed the 1040 EZ. (And my J1 visa ended at 12/31/2012.)
At 7/1/2013, I received the F1 student visa. Now I'm not sure if I still can file 1040EZ for 2014 since it's my 5th year in the state even my visa status is changed. (I stayed in the US more than 300 days ever year since 2010)
Thanks for the help :)

If you were an undergraduate student on the J-1, the university HR steered you wrong, because undergraduate students on J-1 visas retain their NRA status for five years, just like the F-1 student.

If you were a graduate student, then the J-1 duration MAY be only two or three years, depending on the treaty and other paperwork.

On your current F-1 visa, you are back to being a NRA for at least two years and probably three starting in 2013.