" with c and d drive can i convert to ntfs "
Yes you can, but be aware that in some cases the recovery boot C\D has failed to kick start the recovery partition. If you do convert it may be prudent to image the entire hard drive, including the recovery partition to a separate drive, just in case it goes pear shaped if you every need to do a recovery. There will be a hidden partition but essential files will always be written to the "C" drive.
In my opinion.
The best is always to convert "D" and leave "C".
" put it into one drive without losing my stuff?"
Yes you can merge both drives into one, it is very easy to do. Unfortunately you would need specialised software to do it 100% safely and that costs.
Why do you want the filing system to be changed to NTFS?