I upgraded 1.3.5 to 1.4.2 but I don't know how to save the comments? Can you help me?
you don't loss anything if you try
http://coppermine-gallery.net/demo/cpg14x/docs/index.htm#13
I guess you upgraded using an auto-installer like the crappy fantastico panel. That's probably the reason as well for upgrading to cpg1.4.2 only. It's mandatory to upgrade to the most recent coppermine version (currently cpg1.4.8), doing as bmossavari suggested.
It's a known issue with the buggy fantastico auto-installer (please note: not a coppermine bug, but a fantastico bug) that makes upgrades fail. Never use auto-installers, always use the "real" installers provided by the original "vendors" of the apps you have. In the case of coppermine, download from the link provided at the top of this page.