How can my employer change my Andriod security settings?
Your employer is informing you of the security you need to implement on your device to access company mails / apps etc. This is a standard practice to endure that company confidential information is not compromised owing to your not having secure lock screen etc. They are not changing it for you. They are asking you to change it. Going by the screenshot, it's simple - agree to implement yourself those measures or not access college mails etc. 

But, there are variations like BYOD / Company owned device etc, which can exercise far more control on your device. See here for details.

Edit:

From discussion on comments added a very useful input from Izzy. The app which you are installing to read the mail should not have device manager permission as only such apps can do a factory reset (aka Google Device Manager on case of stolen devices)