Hello! To delete a person, you usually need to click on a person, select "More options" on the side menu and then "Delete [first name]" on the bottom of the list. This isn't always possible though - if the person is the only thing that deletes other people to the family tree (i. e. if "Isabelle" is a descendant of your main family, and she has a husband and kids that have no connections to anyone else on the tree, you can't delete Isabelle unless you delete her kids and partner first).
If you just want to remove a foster relationship, click on the foster child, again select "More options" and then go to "Set parents". This shows all parental relationships this person has (probably including both bio parents and the foster parents). Usually, the foster parents would be classified as "Second parents". Go to the field where you can set the second mother, type in/select (none) and do the same to the father if neccessary, save and continue - there won't be any foster relationship displayed on the tree anymore.
However, the same rules apply as above: If your foster parents are only connected to the tree via their relation to the foster child (or vice versa) the relationship can't be deleted as it would split the tree. Instead of removing the relationship, you'd need to either delete the foster child or foster parents altogether. If the foster parents are grandparents or maybe aunts/uncles of the child, there should be no problem.
Hope this helps!
