I have a question about how to change variables in parent shell.

My script, test.sh, is below:

#!/bin/sh
# test.sh
PATH=.

The commands I ran for test:

$ echo $PATH
.:/usr/bin:/usr/sbin:/usr/local/sbin:
$ sh test.sh
$ echo $PATH
.:/usr/bin:/usr/sbin:/usr/local/sbin:

Note that when I run sh test.sh, the variable PATH was not changed. I know that I can run . test.sh to make it change PATH. But for some reason I have to run sh test.sh. So in this case, how to make child process change the variables in parent process?

Thanks.