Follow the steps to do so.
1. Open the UC Analytic Configuration Console
2. Click Manage Deployment
3. Click Modify Deployment
4. Click Edit Properties
5. Click Query Engine Advanced
6. Uncheck the Calculate Memory Automatically and then add more Memory. You may have to use a bit of a process of elimination until you get to where you need to be with out the Service Stopping.
There has been a Enhancement ID to help better manage Memory Automatically you can search the latest version of Release notes for Enhancement ID TF00603637 to see if this has been added.