Why cant I get those memories out my head?

PTSD is a possibly explanation, it's a perminant alteration in your psyche that disallows forgetting these types of memories. The good news is that with therapy and a good thorough plan you can reduce the frequency in which you think about them, and also you can learn to live with them.

It made an impression. Maybe it now affects your daily life. If it was something bad, it may reappear when you least expect and when you hope it wont. The best things to do is to try and put your mind on something else.

They touched you deeply and you have to make new memories to replace the old ones . But the old memories they will not be gone forever, just not so prominent anymore.

There are many times in life when present occurances may trigger memories of past traumatic experiences.

If a certain memory sticks out at you in a certain way, whether it be good or bad, then it might have impacted you in a certain, perhaps unknown, way. If it's a bad way then something that could be done would be to recognize why it affected you that way and get it off your chest to someone close or anonymous. If it's good then hold on to a memry that's precious like that. Those are harder to remember than the bad ones are.

dwelling on them can make them stick around longer. try to get out more, maybe exercise or take up new hobbies to distract yourself.

It would be nice if there was a sort of wonderful machine that hunted memories in your head and deleted them. But that technology isn't exactly available. I've had memories that haunt me, things that I may be better off not remembering. Honestly, (and I know this isn't what you're looking for) it just takes time. In my experience, time allows you to reflect on events. I used to be scared, ashamed, embarrassed, guilty, or haunted by things every second of the day that I don't think about anymore. Every once in a while I remember, though. And while it does stir up some latent memories, it's nice to look from an outside perspective and think, "Wow. This used to consume me every moment of the day." And now I can handle it; life goes on.

If you went through something traumatic, chances are the memories will always be in your head. The question you should ask yourself is, how do you want to proceed from here? The best thing you can do now, is distract yourself with things and remember that if things get rough there are resources. Over time the memories will naturally fade and it will just become history.

I think because you are thinking really hard in not thinking about these memories, you do exactly the opposite.