Don´t worry about the harder difficulties, you will be able to collect tons of items along the way that will make it much easier for you!
Check out the collectibles guide to see where/how you can get those. I´m mainly referring to the ´broken moon pearls´ (increase your magic gauge) and the ´bloody witch hearts´ (increase your vitality bar). Make sure that you have collected as many as possible before you advance to hard mode. That also means that you need to complete as many Alfheim challenges as you can (check out the guide for the locations), since you get either a moon pearl or a witch heart as a reward for completing them. These challenges are also a great way to train yourself, improve your skills. The Alfheims are only availabe in normal mode and harder, I strongly recommend to do them on normal since that will be easier. Buy all the remaining hearts/pearls at the Gates of Hell. There are also accessories that you can buy from Rodin. Take a look at what they do and use them to your advantage!
You will also unlock new weapons during the game, more powerful weapons.
Keep playing, you will get better at it. Don´t worry.
There is the ´flute glitch´ that could help, but if I were you I wouldn´t use it too much since these items are not available in the Alfheim challenges!