Open the image in Preview
Click Tools
Select Adjust Size
Enter the new width and height
Keep or uncheck Scale proportionally
Click OK
Go to File
Select Save or Export
Choose the format and save the resized image
Open the image in Photos
Click File
Select Export
Choose the size option if available
Export the image
Use the Finder Quick Actions if available
Select the image
Right-click
Choose Quick Actions
Select Convert Image or Resize if shown
Open the image in Pages, Keynote, or Numbers
Insert the picture
Resize it by dragging the corners
Export or save the file if needed
Use an online image resizer in a browser
Upload the picture
Choose the new dimensions
Download the resized image