Step 1 :- Click on Icon then click on show location like below
Step 2:- Then edit the eclipse.ini
Step 3:- Then you need to modify below:-
-Xms256
-Xmx1024
Related post.
https://help.salesforce.com/apex/HTViewSolution?urlname=Why-does-the-Force-com-IDE-time-out-or-display-a-Java-heap-size-error-when-I-m-building-a-new-project&language=en_US
http://www.tgerm.com/2012/12/fixing-performance-and-memory-issues-in.html
