at the run command: convert [volume] /fs:ntfs [/v]
For example, convert c: /fs:ntfs /v
If you need more info, type convert NTFS in your help & support, it shoudl give you all the relevant information.
I should warn you that converting from FAt32 to NTFS will leave you with 512 k clusters, which will open you up to severe MFT and file defragmentation. There are other warnings in the help & support page.
I would recommend formatting and clean installing if your able to. This will give you the best results. Trust me, you WILL NOT be happy with a converted drive.