Maximizing Window Issue

I have a problem with Windows that doesn't happen too often, but happens
enough where I'd like to know a simple way to fix it. There are times when I
click the maximize button in a MS Office program and it doesn't maximize to
fit the entire screen. It usually maximizes to the middle of the screen and
that's it. How can I fix this so that it maximizes to fit the whole screen?
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Thank you,

Rachel