Hangie the HDD file is quite large, almost 32 GB when expanded, so better to ave a fast internet connection. I culd make the update because my navi system permits update trought USB port, if your system has not USB you can't. The procedure is rather simple, provided that you have the proper USB memory key , formatted in FAT32.
So the steps are:
order the update giving serial number of navi system
the dealer buys key code from Toyota/Lexus and receives the customized files for your navi
then he sends you by email the key code and the link to download updates
you download the rar files with update and expand them into a USB stick
connect usb and go to update menu , and when asked insert key code on navi system
the update starts , it needs many minutes so you have to leave the car ON (for hybrids not such a problem as gasoline engine keep off most of the time
when you read on screen procedure has come to end you can switch car off and wen restarting you can verify on navi menu you have new map version.