There are many different ways of doing this. If you are asking about the content of a file, use the 'tr' (translate) command. The actual parameters may vary from system to system, so use the 'man tr' command to be sure.
For example, you may be able to change from lower to upper case by:
tr '[a-z]' '[A-Z]' < infile > outfile
P
passwd
Unix is inherently portable; this means that a program, script, or process may be moved from Unix system to Unix system with little effort or change (hence - portable).
The 'CD' command is not standard for Unix. The 'cd' command, however, will change directories (folders). It is a means of navigating the Unix file system.
passwd
Use the command 'passwd'
Because CD is short for "Change Directory"
Back up the files to another disk change the os and restore the files.
There are no actual "hidden" files in Unix. The only way to hide the existence of a file is to place it in a folder that no one has read permissions for.
CD /
Use the following: PS1='$PWD : '
You use the 'chown' command. You must be the owner of the file to do this or the super-user to change ownership.