Step 1: Make sure no other World of Warcraft clients are installed on your computer.
Step 2: Download the game here.
PC Download:
http://tinyurl.com/yguul99Mac Download:
http://tinyurl.com/ykzf7srStep 3: Install the Wrath of The Lich King client, and wait for it to finish downloading.
Step 4: After installing the game follow the other " How to " guides to patch up and play as soon as possible!