In section 5, the link to the Connect and enable external connection and external form features is broken

Hi Dean, thanks for letting us know about the broken links. All fixed now  

I thought I'd share my experience with upgrading (from 4.3.1.1 to 4.3.3.0) and, in particular, the issues I encountered and how I went about resolving them.

Firstly, at step 3 (above), the Solutions Management page was reporting the nintexforms2016.wsp and nintexforms2016core.wsp solutions as Error. The suggested fix is to select the solution, then click the Deploy Solution. However, when I went into my failed solutions I had no such option. Instead, I could Retract Solution -- which I did -- and once the retraction completes I was able to Deploy Solution. Once the deployment completed, both solutions were successfully reporting as Deployed.

However, I still had issues as no Nintex forms were working. For example, when attempting to edit/design a form, I was getting the following error: 

The Expression prefix 'NFResources' was not recognized. Please correct the prefix or register the prefix in the <expressionBuilders> section of configuration.

To resolve this, I needed to re-activate the Nintex Forms feature on the web application(s) as suggested by this blog post. I don't know if this is normal practice for an upgrade (i.e. the feature gets deactivated) or a consequence of the error I experienced. Hopefully this post might help someone in future, and/or perhaps this document could be updated with the additional information on troubleshooting the error, if deemed appropriate.