Before you do anything to drastic, ask your parents. Also, I rearranged, painted, added color and accessories to my entire house, and I drew a floor plan, that then a drawing of each wall. This is a good idea when you are wanting to paint or rearrange, or hang things on the wall.
I have this huge sliding glass door with vertical blinds on it that I couldn't figure out what to do with, so I found some old white Christmas lights and draped them across the top. Its so cool, it they are bright enough where you don't need any other source of lighting.
Your room needs to have a focal point, something in which everything else is based around. Being its your bedroom, your focal point should be your bed. Mirrors awesome for a bedroom, and it doesn't need to be used as a mirror, just decoration. Hanging a square mirror above your bed so it diamonds shaped,
Make a list of the things you like. You can make this fun, and no one has to see it but you. Be completely honest with yourself. Mold your life around what you like. It's alright if you like to make other people happy, it's good to be able to bend a little for other people. However, don't wear something to make someone else like you. Don't do the 'cool' things if you don't like them.
Decorate your room the way you want it to be. If you want certain colors on your walls, buy some paint and get started! Whether you want to hang paintings or posters, or if you want to put flowers or a collection of yours on your shelves, make sure your room reflects you as a person.
Decorate your bedroom with fairy lights or charms, or brighten up a boring bedroom wall with a notice board filled with pictures of all the people and things that are special to you.
One great idea is a beanbag in the corner. Plants are very pleasing to the eye! Find some good posters of nature or peace and such, and put them up on the walls. Put up some poster frames or something of strange objects. Perhaps get a really large one and put a loved but too small T-shirt in it or something. The possibilities are endless! And most of them-like the windchimes or beanbag chair-are fairly inexpensive.
Most of all, have fun redecorating!