CMSimple 4.0 is utf-8 encoded. So you have to convert all contents from your old CMSimple installation to utf-8 without BOM (Byte Order Mark).
For that you need a proper code editor, notepad++ is recommended, this code editor is available for free.
Download notepad++ »
Now open the file ./content/content.htm from your old CMSimple installation with the code editor, and then save it in the format "utf-8 without BOM".
Now upload the file content.htm to the directory ./content/ of your new installation of CMSimple 4.0 or higher. If you don't use plugins, now the update already is done.
Now you can delete your old CMSimple installation (backup made?) and upload the new CMSimple installation to this place. Note, that on many web servers you have to assign the necessary write permissions for folders and files.
If your provider allows, you can simply forward the domain to the directory, in which you have your new CMSimple installation. Then you have not to care again for the write permissions of files and folders.
At the end, you still need to check the configuration, page title, description and keywords (for Google), language, and above all:
!!! CHANGE YOUR PASSWORD !!!