In general, you can't, at least not without making special arrangements. The child can change these values all it wants but the changes won't affect the parent shell, since the child is changing a copy of the original data.
Some special arrangements are possible.
Your child process could write out the changed variables, if the parent was prepared to read the output and interpret it as commands to set its own variables. Also, shells can arrange to run other shell scripts in the context of the current shell, rather than in a child process, so that changes will affect the original shell. I.e. you type .