Hi Sreeni,
You can create a new APS in CMC containing the Data Federation Service with
-Xmx2g -> 8g (This is the suggested range)
Make sure you remove this service from the existing APS and then create a new one.
You could refer SAP KBA 1694041 - BI 4.x Consulting:- How to size the Adaptive Processing
Server (APS)which would assist you in sizing the APS.
Regards,