It is possible to upload your thesis here at ResearchGate, see https://explore.researchgate.net/display/support/How+to+add+research for instructions. If you mean to publish your thesis as a book, see the following discussions:
I would favour attempting to publish as journal article(s) as it is most likely to be read and recognised by people in that field.
It is hard, though, and I think the necessary steps are mainly to find a suitable journal and liaise with the editor to get their approval to do this as it may be quite long and some may consider it to be duplication. The manuscript(s) nay require to be modified from your previous because of length requirement and/or scope of the journal.