Coud you please confirm if the upgrade was successful or did it fail.
If it failed with outofmemory exception then you might need to increase the heapsize.
Mostly you need to increase this heapsize in setupdatabase.xml, but to confirm we can check the log file and identify.
If the upgrade was successfully completed and while starting the server you are facing outofmemory issue then you need to increase the heapsize at application server level. For example in Tomcat we specify the jvm parameter of heap size in setenv.bat file.