NTT DoCoMo generally allows customers to change their mobile plans, but the specific conditions may vary depending on the type of contract and plan currently in use. Typically, customers can modify their plans during designated periods or through specific channels provided by the company. It is advisable to check the details of your current plan and any potential fees or restrictions that may apply to plan changes. Additionally, NTT DoCoMo often provides options for changing plans through its official website or customer service channels. For precise information regarding your particular situation and to explore the available plan options, it would be beneficial to review the current NTT DoCoMo website for the most up-to-date details and any relevant instructions on modifying your plan.