How to ask your employer about a salary increase? When I started worki…

How to ask your employer about a salary increase? When I started working, she said that the first month's salary would be one amount, and then from the second month it would be slightly higher. I have been working for four months now, and my salary is the same as in the first month. I am very stressed and afraid to ask how to put this question? I really respect her and don't want to let her down but this question worries me. When we signed the contract, she said we would make an addendum on salary increase later.