XML Format
To update single record into a module in a single API call :
https://crm.zoho.com/crm/private/xml/Leads/updateRecords?authtoken=Auth Token&scope=crmapi&id=Record ID&xmlData=XML Data
To update multiple records into a module in a single API call :
https://crm.zoho.com/crm/private/xml/Leads/updateRecords?authtoken=AuthToken&scope=crmapi&version=4&xmlData=XML Data
Click Multiple Record Updates to view the sample xmlData and response for multiple records duplicate check.