Note that the current working directory is a per-process resource; the cd command changes the working directory for all interpreters and all threads.
cd [file home fred]
Change to the directory lib that is a sibling directory of the current one:
cd ../lib
Copyright © 1993 The Regents of the University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.
Licensed under Tcl/Tk terms
https://www.tcl-lang.org/man/tcl9.0/TclCmd/cd.html