The only way to achieve this is if you kept a copy of previous versions of the utag.js from the template file.
If you did keep a previous version copy, you can always copy and paste that into the "utag loader" template file and Save to your profile and publish.
So there is no way to choose a version in the sense of a drop down list of any kind, it is a matter of reverting to a previous version by pasting in the older version code if you choose to do so.
To add to Bahman, there may be 2 ways to think of the utag.js "version".
First is his method referring to the actual version such as 4.008 or 4.26.
Second is the environment (dev, qa, or prod) that should load in the page.
If the latter, the environment the page is tagged with will load by default. However you can use the Web Companion tool to switch environments. Craig gave you the link to the Web Companion post and that will guide you on the process.
Is your question related to loading the utag version located in dev/qa/prod? If so, you can use Web companion to switch utag publish targets.
To test a different version, I would recommend publishing within TiQ to a non-prod target (qa or dev) and from there you can either hardcode the reference in a test environment or use web companion to switch environments.
A third way would also be a previous publish branch "version". All of these are very different as how you would go about doing this.
If you need additional help you may want to reach out to your Account Manager for more specifics.