@evelin utag.js should always remain async. However if you have a tag or two that require sync, you can also have utag.sync.js run on your website. This can be enabled under the Configure and Publish settings. The setting is called "Generate utag.sync.js File"
If you are new to Tealium, I would encourage you to bring this up as part of your deployment so one of our deployment engineers can go over the pros and cons of Tealium's sync and async solutions.
Please make sure you understand all of the risks with using utag.sync.js before adding it to your website.