Open your image in PSP and go to ‘File’ > ‘Export’ > Image Slicer.
Click the grid icon on the ‘Image Slicer’ box that comes up (highlighted in red below).
Now on that same box, click your image in the ‘Preview’ window, and another box should appear called ‘Grid Size’. Change your settings to match mine (but customise them if you find it’s wrong for your image):
Make a new folder for your images and HTML so you can find it easily, then press ‘Save’.
Then find the folder on your computer, and upload everything to your site, or you can open the HTML file and take the code out that way.