There are two ways to fix this issue. You can either use an image resize application to resize the image to a lower resolution or change its quality. You can perform the same operations from the same interface. For example, XnView is able to do this. Download the application and install it. Launch the software and open your image then go to Image > Resize or open the file and go to File > Save as > JPG > Options and lower the quality below 60.
