CPU usage High

Hai I run my elasticsearch in version 2.1
I run in server with CPU 2GB. and I have 2 nodes in my server.
I set ES_HEAP_SIZE=256m in my nodes
but when I check use top I get
USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
14784 elastic+ 20 0 2761876 451960 11692 S 74.6 22.1 57:50.59 java
14636 tomo 20 0 2762376 512980 16704 S 72.6 25.0 56:47.55 java
please help me

Add more heap!
How much data in the cluster?

add more heap?
so how much I set my heap
I crawl website an I add to ES

Change that.

when I set to ES_HEAP_SIZE=1gb
Now I get 114% and 60% CPU usage