There are several ways depending on your experience with Xara Photo and Graphic Designer, using the Eraser tool or Masks. Whichever way you choose, it is a time consuming process
This is a general method - I do not have Xara Photo and Graphic Designer, however it is capable of doing this.
Open the image in Xara and then use Save As to create a copy of it, this avoids destroying the original.
Make/convert the image to a layer - refer to the installed PDF manual on how to to do this if necessary.
Either:
1. Using a the Eraser tool, remove all the background, start with a large tool size setting from the edges working towards the person you want to keep as you get closer to the person zoom in and reduce the size of the eraser tool as you go along, also decrease the hardness of the tool to give a softer edge when working close in
or 2. As 1 but using the Mask (Transparency) tool
Keep saving regularly.
Export/save the image as a png file - this should preserve the transparancy you have created.
Import the png image as a layer onto the required image.