If the image file that you want to upload is larger than the allowed size or too big for the alloted slot,you can always resize the image using any
Open the image with the application in a new document.
The snapshot given below is of Photoshop.
Locate the RESIZE option,
This tab will give you the option of changing the size by reducing the image pixels or by percentage.
You can also resize logos by selecting the corners.
You may enter your desired dimensions and save the file.