If your volunteer application status is Pending you are not allowed to make any updates to the application. You must wait until the status has been updated by the administrator in your school district. 

In order to make any changes to your volunteer application you will need to be on the "My Profile" tab:

If your application is in an Approved status you will see a blue "Edit Profile" button :

Once you have clicked to edit your profile you will need to select "Yes" beside of the question that says "Would you like to continue volunteering?":

At this time you can scroll through and make any needed updates in your application - in order to update the school(s) at which you wish to volunteer - remember that your application will have different school options - this is just an example - if you wish to volunteer at more than 3 locations you will have to select the All Schools option(if this option is available for your district) in the drop down box  :

After you have made the necessary changes you will need to scroll to the bottom - click the box that says "I Authorize" because this will show your email address as your electronic signature - and then you need to click the "Save Changes" button: