Can someone advise on how to do this as I need to be able to change the price based on what size the customer has selected.
EDIT: Ok, i need to explore more before I post things...I found out how to do this.
You need to first create variations for the product such as sizes, color, etc. Then when you go back to edit the product, choose which option you want to edit e.g. size XL. Then you can edit anything and it only applies to the one option. So in my case, I change the price of XXL to 28.99 and when they choose that option, they get that price.
So choose a product and in the top right, click add product options. That is where you can make option lists for sizes, color, etc. Then as i said above, go back into edit it and change properties relating to each option and you will be good to go.