Should you need to just replace the file of your paper, click More on the paper's web page on Researchgate, then in the drop-down menu click on Add full text and then add the new file of your paper (before that it's a good idea to make sure that the license under which your paper was published allows you to upload the said new file on Researchgate ). After that, you can delete the old file of the paper in question on the paper's web page on Researchgate.
Source and further details: the discussion: https://www.researchgate.net/post/How-do-I-replace-an-existing-article-in-my-publication-list
This is from Artur Sergyeyev who responded to my query on
January 17
Should you need to just replace the file of your paper, click More on the paper's web page on Researchgate, then in the drop-down menu click on Add full text and then add the new file of your paper (before that it's a good idea to make sure that the license under which your paper was published allows you to upload the said new file on Researchgate ). After that, you can delete the old file of the paper in question on the paper's web page on Researchgate.
Source and further details: the discussion: https://www.researchgate.net/post/How-do-I-replace-an-existing-article-in-my-publication-list