How to Edit Videos in Youbube (e.g. merge) for free
Goto https://www.youtube.com/editor and drag your videos into the field named "drag videos here". Unfortunately then you just see only the one video.
To add an additional video just click on the field marked with the X and then you see again your other videos and you can drag more of them to merge.
After that you go to your channel / video manager: https://www.youtube.com/my_videos?o=U, click on the arrow right of your new video and click on download MP4.
Hope it works.