i'm thinking about getting this

https://www.bikesdirect.com/products/dawes/deadeye.htm

but i dont know what size i am.
i'm 5'4 or 5'5.

If you don't have the ability to figure out what size you need based on the geo specs, you're better off buying from a store where you can test different sizes and models.

I think that bike just fits to your height. I have my bro like that of yours. It was just good as expected.