Upright is one of those annoying programmes where they are part of box sets and catch up at the same time but Sky only give the rights to watch the box sets content on the boxes, not the apps.
This means you have to try and find the catch up content, which is near impossible on some of the apps.
Last time I checked episodes 2 and 4 worked via search but I couldn't get others to work.
If you have a games console it's quite easy to get around but the PC app or mobile is really difficult.