How to Delete Fota files
Step 1: Download the files to your computer and upload them to your your phone.
Step 2: Install any ROOT File Expert
Step 3: Make sure that the File Explorer can mount and write on the ROM system files.
Step 4: Extract fota.zip file and select Unzipped fota files (fota_delta_dp1 and fota_delta_dp2) to /data/fota or paste the 2 files in this folder
Step 5: Reboot phone
Now check your free space in the ROM.