Flashing the update will wipe all data, as in factory reset wipe, as in everything is gone. Poof!
You must update to 4.1.2 before updating to 4.3.
You can not downgrade to 4.1.2 after installing the 4.3 update. Any attempts to do so will brick your device.
Go Here For Rooting Instructions
1) Backup your files to your PC.
2) Odin back to stock 4.1.1 (DLK3).
3) Download update zips for BOTH 4.1.2 and 4.3, and check MD5 for both.
4) Create two folders on your external sd card named 412 and 43, and put the 4.1.2 and 4.3 updatexxx.zip in the respective folders.
5) Plug phone in to AC charger (4.3 update takes a while).
6) Reboot recovery, install the 4.1.2 update from sd card, flash (update installs and phone reboots).
7) Reboot recovery, install the 4.3 update from sd card, flash (update installs and phone reboots).
8) Enjoy 4.3!
The 4.1.2 OTA can apparently be flashed with Mobile Odin.
Download: Stock firmware