I got an .xsd scheme that has multiple root elements, few complex and simple types, complex types refer to those root elements. I can’t generate .xml in a way i want from it because of those root elements. So i think i need to add element that will serve as the root element, and add all other elements as its children, or am i wrong?
Is there a tool that can help me create root element and refactor scheme? What i got:

I was thinking maybe i just need to create another xsd with 1 element and ref all elements form first xsd in it, but i don’t exactly know how to do it. Is this a good idea?
The answer to your edit is indeed, as Pangea said, NO. And that is because to ref another element (as in <xsd:element ref=”SomeElement” … />), the referenced element must be declared globally.
Other scenario that requires global elements is the use of substitution groups. What I am trying to suggest is that it may not always be possible to refactor an XSD in a way that leaves global only the elements you want as root in instance XML.
Which should make you think that to solve your problem, a better way might be to go after the reason why you can’t generate .xml the way you want. If you can describe a bit of that, you might get a better answer here…
Another reason I wanted to add this answer was that I noticed the use of XML as a tag name. While it may seem OK, I can tell you that I’ve seen some pretty “big-name” applications that would simply choke with that <XML/> tag name. XML is actually “reserved”, please take a look at this section of the XML Spec. To quote: “Names beginning with the string “xml”, or with any string which would match ((‘X’|’x’) (‘M’|’m’) (‘L’|’l’)), are reserved for standardization in this or future versions of this specification.“
Always play nice with the specs….