It will raise the pH.
The pH scale goes from 0 to 14. Numbers below 7 indicate a solution that is an acid. The closer you get to 0 the more acidic it is. Numbers greater than 7 indicate a solution is a base. The closer you get to 14 the more basic it is.
If you have an acidic solution like you said, the pH is somewhere between 0 and 7. If you add a base, you take it more toward 14. We can't know how much it will change without knowing some numbers. You could have an acidic solution with a pH of 2 and adding the base will move the pH to be 5 or maybe all the way to 14. How much the pH will change will mostly depend on how much base you add and the concentration of it.