First of all thank you very mutch that you want to contribute to LetterCreator. By submitting changes, you accept that you grant LetterCreator an unrestricted, royalty-free, exclusive right to use your change. If you don't want that, I'm asking you not to contribute any changes. Anyone who contributes changes that are incorporated into LetterCreator has the opportunity to be mentioned in About Site. Unfortunately, there is no guarantee that your changes can be applied.
First create an Issue where you describe your changes. After that create a Pull Request and link to the issue. I will check your Pull Request and the Issue and probably merging that feature or bugfix to productive code.