As you are already on the official SpendLess Daw website, you just need to go to the main page and click on "Download".
Once done, your browser will probably tell you that the ".exe" installer is not commonly downloaded and might be dangerous.
To finalize the download, you will need to follow some steps and find a button that looks like "Keep file".
Note that these steps may vary and be more or less complex depending on your browser.
Once downloaded, launch the SpendLess installer.
Your antivirus will probably indicate the same thing as your browser: the software is unknown.
You will need to manually approve the launch so that your antivirus does not block the application again.
Depending on your antivirus or OS, the complexity may vary, but you can generally approve the launch directly from a popup on your screen.