Hi there,

Simply by uploading the new v.4 via file manager?

This is not possible because EasyDiscuss4.x have many modifications and most of the structured as changed.

I would like to recommend you to first install fresh installation on your test site and migrate all the data to your test site and see how it looks and feels Whether it is compatible with your looks and feels.

For your to install EasyDiscuss4.x is to follow steps stated in this documentations --> http://stackideas.com/docs/easydiscuss/administrators/welcome/installing-easydiscuss-4