You may not want to have Monday as the first day of the week, but perhaps prefer to start your week on a Tuesday.
To do this click "Settings" then "Users" then click the name of the user for whom you would like to make this change, scroll down until you see "Calendar settings" and the section which is called "Calendar start day" as circled below:
If you click the black arrows on the right hand side of the text box:
A drop down menu will appear which will allow you to select the day of the week you would like to use:
Once you've picked the day of the week you would like to start your calendar view from, in this example, I have selected Wednesday:
Scroll down and click "Update user":
This change will then be reflected in your appointment calendar, the week now starts on Wednesday rather than Monday: