In most cases it should look like this.
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Please do all those steps - step by step !
1) Disabe then Uninstall old plg_gkextmenu plugin (!)
2) Upgrade from J2.5 to J3.3.4
3) Re-install template to new version, for J3.x
4) Re-install all gk modules, I mean : mod_image_show_gk4, and mod_news_pro_gk5 - with versions for Joomla 3.x
5) Install plg_gkextmenu and enable plugin which you can take from gk_rockwall_rest_files_J!3 or other packages
But we can not help in migration via support, because each case is different.