If you purchased the game on the WolfQuest website or on itch.io (in both cases, the actual purchase was handled by itch.io):
To download the game again, go to your itch.io game download page. To go there, click the download link in the purchase email you got after purchasing the game.
If you don't have that email receipt anymore, you can have it sent to you again -- input your email address in the 'Recover Purchases' section of this page -- but then keep that email because you can use it again in the future to download the game again.
If you no longer use that email address, you will have to ask itch.io to change the email address on your purchase. Send an email to email@example.com and be sure to tell them your old email address and new email address, and ask them to change it on your purchase of WolfQuest.
Here is some help about how to move game files to a new computer: https://support.wolfquest.org/help/moving-game-files-to-new-computer