you can always change difficulty, unless you care about getting achievements in which you'll have to start over.Well I've not actually done that much fighting yet and already died twice, so it's probably more my poor technique at the moment.
I set it on the difficulty down from that. Can I change it now or is it too late?
you can't just keep hacking and slashing, which is what I did at first as well. as the poster above said you have to use all the tools at your disposal including correctly timed parry/evasion and potions, decoctions depending on which enemy you're facing. though I haven't played this game in a while so it'll be like playing as a new player again when I get back to this game for the upcoming expansion pack, especially with all the new enemies they're going to introduce...