I suggest you to read http://en.wikipedia.org/wiki/Semantic_HTML, it should give you an initial indication of how to improve the quality and meaning of your markup which will also have a SEO benefit.
I would start by adding <h1/>, <h2/> tags around the products titles, subtitles etc.
You would also need to implement URL rewriting to make your URLs user and SEO friendly, since you are using .NET, here is a good starting point http://www.iis.net/download/urlrewrite
Also think of analysing and restructuring the order in which you output the HTML (not the layout, but the markup, with CSS you will always be able to shuffle things so that they appear in the correct position), for instance in the page DetaliiProdus.aspx?c=m1&p=1073&s1=61&s2=157 you have your product copy right at the bottom of the (rather big) page. Think of moving up the markup hierarchy what is more relevant for each page.
Last tip, when thinking of SEO, think it in user terms, what would make it more readable and user friendly for users (they may be using various devices, small screens etc) will 99% work for SEO too!