In order to upload your collection, launch Hearthstone Deck Tracker or HSTracker along with Hearthstone. Click on the "My Collection" button in Hearthstone, and after a few seconds, you should see a banner notifying you that it's been uploaded to our server.
First of all, make sure that you've updated your deck tracker application to the latest version. If a new expansion or update has released recently for Hearthstone, you'll need our latest update to enable collection syncing.
A common issue with this is when the deck tracker gets out of sync with HSReplay.net. Perform the following steps:
Log out of both HSReplay.net and your deck tracker
Log back into both. Make sure the user you are using matches on both HSReplay.net and the deck tracker.
Launch Hearthstone with the deck tracker running
Enter "My Collection" in Hearthstone