Any file you upload must be less than 1MB in size. Depending on what device you're using to resize it, the best way to do so is to make a copy of the image, change the size and save it in ".jpg" format.
To Change Image Size and Type:
Windows
Right click on the image in the folder and select Open.
Press the three horizontal dots in the upper right hand corner.
Select Resize.
Select Define custom dimensions.
Look under Width. If the number in the field is over 1500, enter 1500 under Width:. The height should automatically adjust.
Press Save resized copy.
Go back to the folder with the image, right click on the image and select Properties.
Confirm that the number next to Size: is under 1000KB or 1MB.
If you're having a hard time converting an image to jpg, use this online tool: https://onlinepngtools.com/convert-png-to-jpg ... You'll be able to upload the .png file and convert the file to .jpg and resize it using the instructions above.
MacBook
Open image in preview.
Press Command and A at the same time.
Press Command and C at the same time.
Press Command and N at the same time.
Press Tools in the top navigation bar.
Select Adjust Size.
Enter 1500 next to Width: and press Ok.
Press File and select Save.
Name the file and select JPEG in the drop down menu next to Format:
Press Save.
Go back to the folder with the image, right click on the image and select Get Info.
Confirm that the number next to Size: is under 1000KB or 1MB.