The structure of Master Boot Record only allows to have four primary partitions. There are cases when one needs more than four partitions and for those extended partitions are used. Extended partitions allow having logical volumes within them.
Your sda2 is an extended partition and sda5 is located within sda2. This is perfectly normal. I don't think the word "overlapp" applies here. In your case sda5 occupies all of sda2 space, and is the only logical volume, so it might be questionable if such layout is rational. But it is definitely valid.
To expand sda5, you would need to expand sda2 first, provided you have enough unpartitioned disk space around it.
If you are not very confident with what you are doing I would totally recommend to backup all data first and start using partitioning tool with graphical interface - it will make things easier and more visual. Try using gparted or similar software.