Which of the following is NOT a recommended step to alleviate High Memory Usage in an Appian instance?

Increasing disk space is not directly related to alleviating high memory usage in an Appian instance. Memory usage generally refers to the amount of RAM consumed by the application while processing data and running processes. Disk space pertains to the storage available for files and documents, which does not impact immediate memory consumption.

The other options directly address factors that can lead to high memory usage. Cleaning up old processes helps free up memory resources that are being held by processes no longer in use. Optimizing process models can reduce memory consumption by eliminating unnecessary steps and improving efficiency. Setting a timer for processes to end can ensure that long-running processes do not occupy memory for extended periods, thus improving overall memory management in the system. These actions target the efficiency of memory usage, while increasing disk space does not have the same effect.