: If you are amending multiple years, you must file a separate Form 1040-X for each year and mail them in separate envelopes.
: To claim a refund, you must generally file within three years from the date you filed the original return or two years from the date you paid the tax, whichever is later.
: Use Form 1040-X to correct errors such as filing status, number of dependents, or total income, and to claim missed credits or deductions.
Due to the specific mention of "308 KB," your query may also refer to one of several federal PDF documents of that exact size: Topic no. 308, Amended returns | Internal Revenue Service