If I dye my (dark blonde) hair to a dark brown, then decide I don't like it can I lighten it?
Going to the hairdressers is not a problem, but I don't like my natural colour as dark blonde just isn't for me, so its either dark brown or a light blonde:)
Also will my hair get very damaged by getting it lightened professionally after being dyed darker??

You will be able to have it lightened again if you dye it dark. Yes, having it lightened after that will cause damage. You will probably experience breakage and split ends if you don't care for your hair properly. Maybe you should start w/ dark low-lights and keep adding to them if you aren't sure about a color. Salon's have samples of colors and can advise how a certain color will turn out on your natural shade. Take in a photo of a hair color you like. There are lots of great websites that you can scan your photo into and change your haircolor and style to see what it will look like on you. Print out the photo and take it to the salon w/ you. Good luck!

It's important to communicate with your hairstylist, so that he/she will give you the color you want. It's easier to go darker than it is to go lighter. If you want to go from dark to light blonde, minus the brassiness, you will need to bleach your hair, and then apply a toner.

Bleaching or lightening your hair can cause certain amount of damage if it's not done correctly. If your hair looks damaged or dry, do a deep condition treatment at least once or twice a week to restore some moisture and resilient to your hair.