You can amend or revoke your Islamic will any time before your death. There are also some situations and circumstances that automatically cause your will to be amended or revoked.
When going through a divorce, your will can be modified to the point where any gift given to your ex-spouse can become void.
After getting married, your will is revoked unless it was previously made while keeping the eventual union in mind.
If a new will is written, the old will should be erased so that there are no confusions caused in the future.
The smart thing is to review your will every 5 years or after a major event in your life like marriage, death, birth, divorce etc. These reviews are necessary because you need to integrate changes. You can ask religious scholars or solicitors for advice regarding these changes.