Resizing image file without losing quality

[Romphotog]

Irfanview has worked fine for me for years.

 

[dennybeall]

Might have known someone had to bring up ppi vs dpi again. The comment was a quote from the Photoshop action where the change was made to ppi. The Original Poster was looking to reduce the image file size and the reduction in PHOTOSHOP of the ppi did just that.
If the question was image size the answer would have been different.

 

[KmH]

There was no mention of dpi in your post (#13), nor in mine (#15).
So ppi vs dpi was not discussed until you brought it up for some reason in post #17.

You used the print resolution term ppi (pixels per inch) to quantify image resolution - pixel dimensions (px, no physical spatial dimensions).
We can't change the image file size by changing the print resolution.
We CAN change the image file size by increasing, or reducing, the image resolution (pixel dimensions).