Have you already gotten approval from the IRS changing LLC to C-Corp? In addition, file the necessary paperwork change to the State Government Office. An example would be notify California Secretary of State and file for change of entity structure in California.
If you have already done the paperwork for entity change. Yes, you will need to file the final LLC up to the date you changed entity structure. I don't know if the LLC is a Single Owner LLC or Partnership? You business is defaults to be taxes as self-employed Schedule C if you were a single owner LLC, a disregarded entity by the IRS. For Partnership, would file 1065 form. Then, file initial C-Corp 1120 tax return for 2017 (if company is using calendar year not fiscal). Besure to W-2 yourself in the C-Corp.