I'm pretty sure in-game tutorial teaches how to extend the biles. Did you read it? Was there something you didn't understand? Maybe it would be easier if you said what was so unclear about it.
You can also try to look for answers here:
viewtopic.php?f=5&t=11605Chapter 3. Gluttony and humours
I'm also pretty sure you have already read it (of course you wouldn't do something as silly as come here and ask basic questions which are answered both in sitckied guides and in game if you could understand them), but still somehow weren't able to comprehend them. So please tell us which part was so complicated so that we can make it easier to understand