There seems to be some confusion online as to whether Singer ever produced a model named the 2502c.
Whether or not they did, there are still plenty of sites you can check to see if a manual for such a product exists. First, you could try safemanuals.com/user-guide/SINGER.
The safemanuals site claims to provide free downloadable copies of every manual it retains, so it's a good a place to start as any.Have you approached Singer themselves? If not, try singerco.com/accessories/manuals and type in your model's details. Look under 'support and resources' for the manual section.
If you've no luck, you could try one of the general sites which act as online repositories for old machine manuals, such as homeappliance.manualsonline.com, manualslib.com.
Or ismacs.net/singer_sewing_machine_company/manuals.
There are several online communities dealing with fixing machines or sewing in particular, where you could jointhe forum, then post a question asking for help. Such sites include fixya.com, sewusa.com and mastersewusa.com.
For a Blurtit answer to a similar question, check In need of a free singer 2502C sewing machine manual. PDF or pamphlet?
Or, if you're just getting started with your Singer, watch this YouTube tutorial produced by the company themselves: