When successful you should get this output.
pi@raspberrypi ~ $ sudo rpi-update
*** Raspberry Pi firmware updater by Hexxeh, enhanced by AndrewS and Dom
*** Performing self-update
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 10185 100 10185 0 0 29302 0 --:--:-- --:--:-- --:--:-- 32333
*** Relaunching after update
*** Raspberry Pi firmware updater by Hexxeh, enhanced by AndrewS and Dom
#############################################################
WARNING: This update bumps to rpi-4.0.y linux tree
Be aware there could be compatibility issues with some drivers
Discussion here:
https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=113753##############################################################
Would you like to proceed? (y/N)
*** Downloading specific firmware revision (this will take a few minutes)
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 0 168 0 0 111 0 --:--:-- 0:00:01 --:--:-- 139
100 46.7M 100 46.7M 0 0 37123 0 0:22:00 0:22:00 --:--:-- 203k
*** Updating firmware
*** Updating kernel modules
*** depmod 4.0.6+
*** depmod 4.0.6-v7+
*** Updating VideoCore libraries
*** Using HardFP libraries
*** Updating SDK
*** Running ldconfig
*** Storing current firmware revision
*** Deleting downloaded files
*** Syncing changes to disk
*** If no errors appeared, your firmware was successfully updated to a51e2e072f2c349b40887dbdb8029f9a78c01987
*** A reboot is needed to activate the new firmware