Beating Lower-rated players

Depends on what you're doing wrong and what your strengths are. It could be different problems.

But, for example, the correct mindset for me is something like:

1) Don't try to avoid equal positions. If it's 0.00 from move 10 to move 60 that's fine as long as...
2) Avoid symmetry. It doesn't have to be opposite side castling, but small things like structure and piece placement. If you keep the pressure on, they'll eventually screw up.

But like I said, it depends on your strengths. If you're awful at endgames for example, then you'll probably have to approach this differently. Some people emphasize unorthodox positions, or attacking positions. I try to be more of a technician. I guess find the essence of your play and emphasize it without worrying about a quick win or early advantage.

Also, beating people rated a lot higher than you while also losing to people rated a lot lower than you is normal for a very aggressive and speculative style, so there may be nothing to fix in the first place.

IDK i have the same problems can barely beat anyone higher then 1500  

This happens a lot to me when seeded 1 or 2 for my section

it's because everyone rated lower than you is a sandbagger. Ok so I joke only like 75% of people are sandbaggers. Other people might argue that you shouldn't expect to beat people 200 points higher than you "all the time" without practically being a national master rating yourself. It becomes more apparent in your admittance of not being able to beat 1800s consistently. In short the 1800s are doing to you what you do to NMs so your inbetween rating seems accurate.