Where to edit main virtuemart page title?

It must be there , click Shop tab then Shop sub item. It may take little longer to load.

It is fully loading and there is only "Additional Information" subitem in shop item, no shop subitem.

May be there any other way to change that title?

No, that means that your vm is damaged. I check to be sure even VM latest version (becuse they change things often). That was always there