I trademarked and copyrighted the plural form (s) of the company's name. Now, I deleted the "s" from the company's name to go with the singular form. The logo is just cool fonts. Do I have to trademark the singular form within the same class that I did for the plural form? Do I have to copyright the singular form design (its the same design but singular without an s)?
Short answer yes. For a trademark to be valid, it must be used in commerce. If you are no longer using the plural mark, your registration will most likely provide you no protection for the singular mark. So it needs to be re-registered.
As to the copyright, usually logos are not protected by copyright unless they are significantly artistic. A trademark is usually what is used to protect a logo. In the case that your logo is covered by copyright, a new registration would be required to bring the benefits of the registration to the new logo.