Launch the WebSphere Application Server Administrative Console.
In the left-hand navigation pane:
Expand Servers then Server Types.
Click WebSphere application servers.
On the Application servers screen, click the server name link.
On the Configuration tab, under Server Infrastructure, expand Java and Process Management.
Click Process Definition.
Under Additional Properties, click Java Virtual Machine.
In the Initial heap size field, enter the appropriate number based on considerations for your environment, such as deployment size, projected system load, desired performance, and scalability level. For example, if you enter 2048, this indicates an initial heap memory size of 2048MB. This setting might result in slightly longer startup times than lower settings but will front-load the initialization of WebSphere memory after a server start up.
In the Maximum heap size field, enter the appropriate number for your environment. For example, if you enter 2048, this indicates a maximum heap memory size of 2048MB, the recommended setting for production systems. Oracle recommends that the Initial and Maximum heap size settings match.
Under Generic JVM arguments, type (as all one line):