When parties make a contract they can add to it or change by writing a legal addendum. An addendum doesn't replace the original contract; usually, it simply changes minor details that have been incorrectly stated, such as a delivery date or a salary, though it can be used to change more important terms. Generally speaking, anyone can draft a simple addendum without legal counsel. However, if you wish to change the contract extensively, the contract is important or there is a lot of money at stake, it is better to seek the help of a lawyer.
Read the contract that you wish to amend. Make a note of the clauses that you wish to delete, add to or change. Next, create a new blank document. Name and style the document "Amendment to Contract." You can set out your addendum any way you like – for example, as a letter or matching the font, style and layout of the original contract. You may wish to use one of the many templates available online.
Define the contract the addendum will change. For example, if your original contract is an employment contract made between Business X and John Doe dated June 30, 2014, write as the first paragraph of your addendum: "This amendment is made between Business X and John Doe, parties to the employment contract dated June 30 2014 ("the Original Agreement")."
Write down the clauses in the original contract that you wish to delete. Use plain language, for example: "Item 12 of the Original Agreement shall be deleted."
Describe in detail the items in the original contract that you wish to modify. Describe the change in clear, concise words, for example: "In Item 4 of the Original Contract the word $60,000 shall be deleted and replaced with the word $65,000." Alternatively when writing an amendment, copy the clause from the original contract and show any changes using bold text and strikethroughs. For example, write: "Item 23 of the Original Contract shall be modified by the following additions indicated in bold and deletions indicated by strikethrough." Then add the bold and strikethrough text.
Make long and complex changes by replacing the old clause with a new one. For example, write "Item 8 is replaced in its entirety by the following:" followed by the redrafted clause.
Write in any new items. For example, write, "The following Items shall be added to the Original Contract" followed by your new clauses.
Add words that make it clear that the original contract is still valid. For example, you might use the following words: "Except as set forth in this Amendment, the [Original] Agreement is unaffected and shall continue in full force and effect in accordance with its terms. If there is conflict between this amendment and the [Original] Agreement or any earlier amendment, the terms of this amendment will prevail."
These should contain a blank space for each party to sign his name and space below that where each party should print his name and business title, for example "Head of Human Resources." Proofread and print the addendum. Have the original parties sign and date it.
Attach the original contract to the addendum. This makes the addendum easier to read and understand.
Have an attorney look over the addendum to make sure it is airtight.
The addendum becomes effective on the date the parties sign it. If you want the changes to take effect at a later date, make this very clear in the addendum. For example: "This addendum shall become effective on January 1, 2015."