how to submit a patch set 2 (or greater) to gerrit?

Forgive me for being a dummy in this matter:

For some time now I submit via gerrit and no longer to the dev-list with an attached patch.
I submit with ./logerrit submit, as described in 
https://wiki.documentfoundation.org/Development#Using_Git_for_LibreOffice_development

I can't work out how to update a submitted patch.
I tried ./logerrit resubmit, but that resulted in a second separate gerrit change (see 
https://gerrit.libreoffice.org/#/c/1533/ and https://gerrit.libreoffice.org/#/c/1278/).

The git push etc. lines in the documentation pages on gerrit.libreoffice.org scare me more than 
that they help me (my fault, I know).

Is someone willing to try to explain it to me in simple terms, preferably with the above patch as 
an example?

Thank you very much!

Winfried