Well you could export and then import using my extension,
but that will basically sort whatever is in each bookmark folder
so if you don't have things in folders it might not work well.
https://addons.opera.com/en/extensions/details/bookmarks-import-export/
Also, they will end up in imported bookmarks, and like I said the names
will be sorted a-z inside folders,- it also won't delete existing ones
so try it first before removing your bookmark file from your system.
THANK YOU very much, I have now been able to export my books marks to a html file, pity the programmers couldnt do this in v 25, what a load of wasted time, . APPRECIATE that someone knows what they are doing and are a help .. Blessings