IBM 5150 Manual To Operations page 151

Here's how to change the name:
1
Make sure DOS is ready and A> is displayed.
2
Insert the diskette with STOCKS.DA T on it into drive A:.
3
Type this:
rename stocks.dat assets.80
Check your typing, and then press Enter.
Notice that the "old" name is first, then a space, and
then the "new" name.
4
In a moment, DOS displays the prompt, A> , and the file
has been renamed.
5
You can check to see that the file has really been
renamed by typing:
dir stocks.dat
This should be displayed:
File not found
Then type:
d
i
r assets.80
Now the information about that file should be displayed.
DOS 3-77