Teressa,
The size of report plays a vital role. More the size of report, more the heap size of JVM would be required on your machine.
You can increase java heap size by using command -Xms1024m -Xmx1024m; where Xmx is the maximum value which depends on your system memory.
Also the Java version (especially upgrade) need to be compatible and supported with the BO version.
For same version, multiple upgrades are provided by Java on regular basis; however, it is not necessary that they have been tested and confirmed by BO developer team.
Regards,
Yuvraj