// Create a client
AmazonS3Client client = new AmazonS3Client();

// Set Canned ACL (PublicRead) for an existing item
client.SetACL(new SetACLRequest
{
    BucketName = "SampleBucket",
    Key = "Item1",
    CannedACL = S3CannedACL.PublicRead
});

// Set Canned ACL (PublicRead) for an existing item
// (This reverts ACL back to default for object)
client.SetACL(new SetACLRequest
{
    BucketName = "SampleBucket",
    Key = "Item1",
    CannedACL = S3CannedACL.Private
});

// Create a client
AmazonS3Client client = new AmazonS3Client();

// Retrieve ACL for object
S3AccessControlList acl = client.GetACL(new GetACLRequest
{
    BucketName = "SampleBucket",
    Key = "Item1",
}).AccessControlList;

// Retrieve owner
Owner owner = acl.Owner;


// Describe grant
S3Grant grant = new S3Grant
{
    Grantee = new S3Grantee { EmailAddress = "sample@example.com" },
    Permission = S3Permission.WRITE_ACP
};

// Create new ACL
S3AccessControlList newAcl = new S3AccessControlList
{
    Grants = new List<S3Grant> { grant },
    Owner = owner
};

// Set new ACL
SetACLResponse response = client.SetACL(new SetACLRequest
{
    BucketName = "SampleBucket",
    Key = "Item1",
    ACL = acl
});