The Logo shows in low quality.

Hi people,
Having a lot of problems with the logo on my web.
No matter what size in pixels I make it the logo always looks very bad (you can see the px)

I have already used png, gif and jpg in a lot of different sizes, but it always looks or too big or with the ugly pixels everywhere.

I would like to upload a logo that is 600px width for example and after put it in the logo slot to be 300px, so this way i will see it without the quiality loss and I will have it with the size i want (300px)
But I dont know how to do that, I have searched a lot before asking and all the info that I found didn’t work.

Is there a better way for that?

I am using a theme called Composer, it is a child of Omega Theme.
Please help me because i just don’t know what more to try.

Sorry for my bad english.

You can see the web here.

EDIT: In the Link you will find the logo in good quality inside the content of the page and the bad quality logo in the header.