Sumithra
at the bottom of the normal parameters sections, you should see a collapsed section called "Job Options". Click on this line and it will open up the settings for memory, # vCPU and how long to wait for the job to complete. Since your gct file is fairly large I would suggest trying 16 or 32 GB. As GSEA is single threaded adding CPU is unlikely to change anything. For walltime you can pick a longer value than the default 2 hours since it will not cost any extra if it completes early, but it's probably not really necessary.
FWIW sometimes the "EC2 instance terminated" messages can have other causes so its not certain that it is memory related. We use AWS spot instances for the compute which keeps costs down, but it does mean that when Amazon's computer's are busy, sometimes machines can get taken away from us. to be given to higher paying customers. We see this a lot around black-friday and christmas sale times and its possible that all of the labour day online shopping (in the US) could cause this at this time of year. Also be aware that the more memory/CPU that you request, the more likely this is to happen.
Hope this helps
Ted