DosChDir

#define INCL_DOSFILEMGR

USHORT  rc = DosChDir(DirName, Reserved);

PSZ              DirName;       /* Directory path name *
ULONG            0;             /* Reserved (must be zero) */

USHORT           rc;            /* return code */

Example 

This example changes directories to \os2\system. 

#define INCL_DOSFILEMGR

#define PATH "\\os2\\system"
#define RESERVED 0L

USHORT rc;

   rc = DosChDir(PATH, RESERVED);