I am still in the learning phase of kitesurfing and on Saturday I went out in the morning. It was quite gusty and I found my kite a little hard to control. I got dragged around a few times and when coming back to shore I realised that the depower on the 5th line was all the way out. If I pulled this in would it have helped depower the kite and give me more control?

You are still learning and going out in easterlies??? Dangerous???

my advice is get a few lessons by whomever is in your local area. It is worth it's wait in gold if you get a good instructor. No offence but it sounds like you need one, cause if you have had previous lessons he or she did not show you all the rope's.