Can't upgrade CB 1.9.1 to 2.1.2

I now have to do this via FTP, since I have no access to the site. Can I simply ftp the unzipped CBLib folder into the Administrator/components/comprofiler/library folder? The contents are radically different

More than likely it's the admin module blocking backend. Disable it by renaming the below folder.

/administrator/modules/mod_cbadmin

Next see if you can access backend again. If still can't it's probably the below system plugin, which you can rename to disable it.

/plugins/system/communitybuilder

CBs library also is not installed to that location, but is installed directly in Joomlas /libraries folder starting with CBLib folder and is a different Joomla package not included with the com_comprofiler zip.

I couldn't find either of the folders you mentioned; I have installed them manually, as well as the CBLib folder; all to no effect

There is no such thing as installing them manually. Joomla doesn't recognize them because they've no row in the extension table. Your last resort is to rename CBs component folders and block it from loading. This is done by renaming the below folders.

/administrator/components/com_comprofiler
/components/com_comprofiler

If you've experience with phpmyadmin you can also navigate to your database table _extensions and simply unpublish CBs extension row.

I now have CB 2.1.2 installed, after a series of processes; however, the fields databasew check show an error in the fb_userid field and when I click the fix button I get the following error:
'BLOB/TEXT column 'fb_userid' used in key specification without a key length SQL=ALTER TABLE `#__comprofiler` CHANGE `fb_userid` `fb_userid` text'
I have tried editing this field in phpadmin with the same query result

I have upgraded CBSubs to the latest version; the CBLogin form now displays a message below the form 'Module Version <> CBSubs version.' This seems to refer to mod_cbsubscriptions; I have the latest version mod_cbsubscriptions-4.1.0+build.2017.05.19.15.39.30.520d1fe23.zip
but this fails to install, as does the cbpaidsubsbot joomlaplugin_cbpaidsubsbot-4.1.0+build.2017.05.19.15.39.30.520d1fe23.zip
Also, the 'Your Profile' and 'Edit Profile' menu items link to a blank page; (I have edited these menu items to display the correct menu-types, which were missing after upgrade)