Config php rename

I have the latest download and the instruction
to rename the config sample php is a problem

After renaming the file becomes a text file instead of a php file
Have tried many ways to rename the file – not happening still turns into a symbol of a blank page and is a text file

My page editor is ok but will not hold the original php file after the rename — the result is that the system will not operate as it is dependant on the file staying in a php form

Seems such a simple thing but has me stymied

Regards Lennie G