My best friends family is like a second family so I spend most of my time at her house. The first time I ever experienced anything odd in my friends house was one time last summer when we were home alone early in the morning. We heard thumpings coming from the wall where her little brothers room is. She has a cat but he was in the room with us so we knew it wasn't that, neither of us made a big deal out of it but we were pretty scared.
A few days ago we were home alone again except this time in the afternoon. We were sitting on different couches and when I turned to look at the TV I saw a little boy standing at the end of the couch. I couldn't really make out any details except that he was wearing a light blue shirt and had light colored hair, he disappeared after a few seconds. I didn't scream or yell but I got up and sat on the couch with my friend and just whispered to her what I had seen. We both went to her room and she started telling me about how one night she woke up in the middle of the night and thought she saw someone tanding at the end of the bed. I think both of us were pretty freaked out but we decided not to talk about it while we were still in the house to avoid making ourselves more scared. So my friend gets up and turns on the shower, she was standing in the dooway to her room telling me about something when we hear a huge slamming noise come from her little brothers room. After that we went to my house because we were really scared.
Both of us told her mom about what had happened the next day and she admitted to us that she had seen someone walking downn the hallway christmas morning. Is there anything we can do about this? Or a way to get rid of this spirit?

You need to speak to the spirit in a calm and kind but determined manner.
You need to explain that they have died and tell them they need to move on to the other side as there they will find family and friends who love them.
Explain that this is your home and you would like them to go now to a better place where other spirits live in peace.

If that does not work,you can do a physical house cleansing and there are numerous and varied on line links to show you how that is done.

I agree with artlady, try to send them to the light, if you are comfortable doing it, but you need to do it in a loving way, coming from your soul, not your ego. You can do a blessing with sage if that doesn't work, or even if it does, just to clear out any residual energy that you don't want there. Good Luck!

I'm just scared that addressing the spirit and acknowledging it will make things worse.. since I posted that my friends has seen a lady walk past her door. And she's heard knocking at her door

I don't know that it would make it worse because not acknowledging it could make things worse if it wants to be noticed.. I would check into paranormal researchers in your area and see what they think, there might be some good ones in your area : )