Use of wrong/wrongly.

My friend and I are having a debate as to which sentence is correct.

Person 1: I spelt grammar wrong.

Person 2: I spelt grammar wrongly.

We are also arguing on the use of spelled or spelt in the above sentences. Can it be used interchangeably?

e.g.       I spelled/spelt grammar wrong/wrongly.

Any help on resolving this would be great as we are at each other throats over this.

Please allow me to add a comment to your explanation.  In the context of the posted sentences, most people would use adjective such as “incorrectly” or “inaccurately” rather than “wrongly”.  

If someone is accused and prosecuted of a crime he never committed, then he is said to be wrongly/ wrongfully prosecuted,

I think people in the United States can undnerstand "spelt" without any problem.

In American English, wrong is accepted as an adverb and is also commonly used that way.  So the most common correct version of your sentence on this side of the pond would be this:  "I spelled grammar wrong."