How do I uninstall the macOS Sierra Installer?
There’s no uninstallation procedure. Despite the .app extension, Install macOS Sierra.app is essentially just a disk image waiting to be installed…no system modifications were made by merely downloading it, so deleting it is all that’s needed for removal. 

That said, as Avery Chan mentioned, you still need sufficient privileges in order to remove it. 

The command rm -r /Applications/Install\ macOS\ Sierra.app won’t execute without prepending it with sudo. But using sudo requires an administrative, master, or root password...

The advisable solution is to ask the system administrator to remove it. That said, if this isn’t possible, a few workarounds exist:

Reset The Admin Password (note that if Filevault is enabled, this won’t work):


Boot into your Recovery Partition holding down command + R at the startup chime
Select Terminal from your Utilities Menu Bar
Enter resetpassword in the prompt. 
From the window that appears, select your boot volume and the administrative account. 
Type in a new password for the account. Confirm the new password.
Click Save, close this pane and quit Utilities
Select your boot volume when presented with "choose startup disk" and then reboot your machine.


That’ll allow you to access the admin account and subsequently delete the Installer. 

Use Single User mode (if Filevault is enabled or a firmware password is set, this won’t work either). While using this method will allow you to remove the file without resetting the admin’s password, it’s not advisable to make filesystem modifications at all in this manner, so proceed at your own risk. 


Hold down command + S at the startup chime. After each of the following commands, hit enter.
Always run a disk check first in SU mode by typing in /sbin/fsck -fy. Don’t be alarmed by output such as “FILESYSTEM WAS MODIFIED”, that’s normal. It just means the filesystem was repaired. 
Now, mount the boot volume with user write permissions. /sbin/mount -uw /
cd /Applications to migrate to the relevant directory. 
Type in echo $(rm -rf Install\ macOS\ Sierra.app) before directly running it. Using actual backticks to nest the rm command is preferable to $(), I just can’t format it properly here. 
Now proceed to remove the installer rm -rf Install\ macOS\ Sierra.app
Type in reboot