Can I use my own merchant account?

I want to use an existing merchant services..can I do this on my forms?

If I understood you correctly you want to set payment field inside of your form. 

If you want to have payment fields inside of your form you have to use one of JotForm payment tools. 

Inside of this articles you can find out more about payment tools and how to set payment form:

http://www.jotform.com/help/47-Order-Form-Basics 

http://apps.jotform.com/category/payment_processing 

http://www.jotform.com/help/165-Setting-Up-Your-First-Order-Form 

If I did not understood your question correctly, please explain in more details what you are trying to achieve.

Let us know if you need further assistance.