This depends on where in the tree the person you want to delete is. You cannot remove a person who is connected to anyone else either through birth or marraige without deleting the associated relatives as well.
To do this you would have to trace through your tree (either up or down) until you find the end and then delete all connections from that point until you reach the person you want to delete.
To delete someone at the end of the tree branch, select the 'change or delete' option in the add relatives section. This will give a second menu. From the options choose 'Delete xxx' ( the name is listed for confirmation). This should delete the person at the end of the branch. If you try to delete someone who is not at the end of the branch you will receive a message saying 'This person cannot be deleted'.