Actually, golds don't have access to redeem or noclip. Also, sprays can be any dimension (1x1 or 1900x1900) they just have to BELOW 250kb. A good way of reducing an image size is shrinking it, obviously the lower resolution/quality the lower the image size. If you open a png file in paint.net for example, you'll see this when you try to save the image:
You can adjust the image size or canvas size to reduce the file size until it reaches 249kb, or mess around with the bit depth. Once you get there you can save the image and upload it to imgur and do as welchnome as stated.
Here's an example of me lowering an image's Bit Depth to make it compatible to use as a spray.
Lowering Bit Depth from Auto-detect (32-bit) to 8-bit
Save and upload to imgur and you should be good to go