I already have Ubuntu 14.04 installed on my laptop. But it's not working properly. I've a related thread here. I urgently require an audio/video cutter like ffmpeg, avconv etc. to be installed which isn't happening in the current system. So, the need to install a fresh one where I will install the cutter.I want to install again the same OS but where! For that please look at my existing hard disk in my laptop.See, I've Windows on sda2 & sda3. But it's not working any more & so I'm interested to delete sda2 & install the new Ubuntu 14.04 there. But I need 3 partitions for the new installation. If I delete sda2, then can I install Ubuntu 14.04 by creating 3 partitions? I'm doubtful as already there is 1 extended & 3 primary. So, if I delete one primary (sda2), then how to get the 3 partitions as logical partitions can't be made inside primary!!Another method: Just now something striked my mind. Shall I create only root (or boot even required) partition on sda2 & use the other partitions  (/home etc) from the existing ones?
How to install Ubuntu 14.04 alongside the same existing OS in laptop?
system installation;dual boot
Why would you need 3 partitions? You only need one. Either sda2 or sda3 are big enough for a normal installation. The new installation normally will overwrite your boot sector, if you don't want that make sure to deselect that option. In that case you will have to bootin the old 14.04 and run update-grub for it to find the new 14.04 and add it to the grub menu.