Having completed all the Soulsborne games (except the new one), my advice if you are struggling is one of 4 things:
1. You are not levelled enough for the area.
2. Your weapon is not strong enough for the enemies (either under levelled or perhaps just not suited to their defences).
3. You need to spend some time learning the level/boss attacks (just to recognise what is coming and whether you should dodge/block/run away from it).
4. You may need to consult a map if it is a really tricky, sprawling maze type level, with few bonfires.
The games are not difficult as such, providing you follow these rules. I cannot complete any other games on hard - I usally play on easy/medium difficulty.
For example, I was really struggling against Maneaters - I could barely get the first one to 75% health before the other showed up and destroyed me - I was a melee build. I went away, levelled up a bit, really improved my ranged attacks, equipped the thief ring and went back and managed it in a couple of goes. Other times, the levelling/weapons do not make so much difference, it is just about knowing how to react to a boss attack and you can just wear them down.
I did find that Demons Souls became easier as I went along - I was quite worried about the endgame, but after two thirds of the game, if you have been levelling properly it becomes more routine. I probably found the first third the hardest, if that helps.