JayData sends the MERGE or PATCH requests based on the dataServiceVersion property of the odata provider configuration.
$data.initService('/odata/$metadata', {dataServiceVersion: '3.0'})
2.0 causes MERGE and 3.0 causes PATCH requests to align with the WCF Data Services OData implementation.
If this behavior does not meet the WebAPI OData requirements, there is a second customization option to determine the kind of the request:
$data.initService('/odata/$metadata', {UpdateMethod: 'PATCH'})
You can make a try to modify the PATCH
to UPDATE
HTTP Verb