If you are using MacOs, you can use Preview to compress images.

Method 1:

Method 2:

You can also use Photoshop to reduce the size of an image.

Method 1:

Method 2:

Open the picture in Photoshop.
Click on File > Export > Export As.
Under file settings, lower the quality slider. As you move the slider, the estimated size will show in the left column next to the image name and size.

You can use an online tool to compress images called Compressor.io.

How to Resize Files