Is there are a way to upgrade PhpStorm 7 to PhpStorm 8 on Windows 7 while keeping current settings ? or do we have to uninstall 7 and install 8 after exporting settings ?
Just install v8. On first launch it will ask you for your settings and will automatically offer to import them from v7. That's it.
Once you happy with v8 you can uninstall v7 (tick the box so it will remove all settings/caches/index files that belong to v7).
Surely: you can uninstall v7 in advance -- but keep the settings during uninstall process. In such case you will have to remove v7 settings manually after importing them into v8 (as described above).
Another alternative is:
File | Export Settings...)
File | Import Settings...and import your previously saved setting.