H1B Changed to F1 Mid-year

You will file as a resident because you qualify under the substantial presence test.

To meet the test you must be present in the USA on at least,

1. 31 days during the current year, and
2. 183 days during the 3-year period that includes the current year and the 2 years immediately before that, counting:
   • All the days you were present in the current year, and
   • 1/3 of the days you were present in the first year before the current year, and
   • 1/6 of the days you were present in the second year before the current year.

Click on the link for more information

Substantial Presence Test