If the position you are considering is the same grade as your current position (e.g., grade 8 to grade 8), your salary may or may not change based on the accountabilities and requirements of both positions.
Promotion to a higher grade position (e.g., grade 8 to grade 9 or higher) usually results in a salary increase depending on hours worked and the grade of the new position.
Similarly, moving to a lower grade position (e.g., grade 8 to grade 7) may result in a reduction in salary, again dependent on hours worked and position grade.