1. First, check the policies and requirements related to credit card limits on the official websites of Industrial and Commercial Bank of China and China Merchants Bank or by calling the customer service phone number.

2. Secondly, according to the requirements of the bank, prepare the required materials, such as income certificate, asset certificate, etc., and apply to the bank to increase the credit card limit.

3. Finally, wait for the application result within the time specified by the bank. If necessary, contact the bank's customer service to follow up on the application progress and understand whether supplementary materials are needed.