When the data warehouse runs out of memory, usually you can resolve the issue by changing the amount of memory available in kitchen.bat (kitchen.sh for Linux).  There's a line in that file that looks like this:

if "%PENTAHO_DI_JAVA_OPTIONS%"=="" set PENTAHO_DI_JAVA_OPTIONS=-Xmx1024m

Try increasing the value until your refresh is able to complete.

If that doesn't work, the other possibility would be that there's not enough memory available on the machine itself.  In that case, you'd have to monitor your system memory usage to verify that was the issue.  To resolve it, you'd have to get more physical memory, reduce the applications running on that machine, or run the refresh from a different machine.