Hi ,
I want to remove tabs in itemform, so all fields shown in form popup sequentially below each other. is it possible or not? if yes let me ask you tell me how.
thanks a lot,
I use joomla 3.4.1 and k2 2.6.9

You can override the item's form in the frontend and remove the tabs markup. In your position I would not alter the backend form, since there would be a risk of losing changes when you update.

More on overriding can be found here: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates