Alternative update + Magento update

Step 1

If you are using WordPress, you should go to your Plugin's list, deactivate and delete the Nextend and Smart Slider 2 plugins.

If you are using Magento, go to your Magento Connect Manager, and delete the NextendSmartSlider2 and Nextend extensions.

If you are using Joomla, you don't need to do this step.

Step 2

Install Smart Slider 2 the same way, as you did it the first time. Your sliders will stay.

Step 3

Go to the Global settings -> Cache, and click on Refresh Slider.