You can download the update directly on your device through the Apple App Store or by using the link which follows:
Users can now capture up to 15 seconds of video with the new micro-video capturing feature introduced on Instagram for iOS. The video has a minimum record time of 3 seconds and like all things Instagram you have a selection of 13 custom filters which can be applied to these videos. These filters range from black & white, to the various color pop, and vintage options.
Once you capture a video you can name it and tag it with hashtags and post it on your Instagram feed. Videos will play automatically when you reach them on your feed, but they won't loop as they do on Vine. Additionally these videos will natively on your Facebook Timeline.
Once you have captured the video, its first frame is assigned as the Cover Frame, and users can select a frame of their choosing to represent their video. Instagram for iOS will also have a feature called Cinema, which is a video stabilization add-on for your short videos. Cinema will initially be exclusive to iOS and will only work with the iPhone 4S and the iPhone 5.
The update has still to be released for Android, but should arrive shortly.