I tried to upload a screen shot of error message with 4Mb capacity using image link, but failed. How I will solve this problem?
Ask yourself whether the full resolution image is actually necessary... in most cases it's probably not.
There is a limit to the file size that can be uploaded using the native IMGUR uploader on Stack Exchange. It's roughly 2MB as suggested by the upload dialog:
Reduce the file size in an external program before uploading.
Also, users are inherently throttled in their participation depending on their reputation. More reputation leads to more privileges which leads to more freedom (and responsibility). While this doesn't relate to image size, such limitations hopefully educates the community in terms of the suggested site behaviour.