Upgrading to 8.3 should not cause the transaction log to start growing excessively in size. The transaction log records all transactions and database modifications made by each transaction. While there may be some growth due to the upgrade (since we periodically make changes to the database schema), growth should level off after that. I recommend truncating the logs, and possibly shrinking them, depending on how big they ended up getting, and watching for growth. If you're using the simple backup model, transaction logs are truncated when a checkpoint occurs. If you're using the full backup model, transaction logs will continue to grow until the transaction log is specifically backed up. 

If after truncating you find that the log continues to grow, you'll want to open up a case with Support so they can help track down the issue.