Definitely off topic but I feel compelled to answer anyway. Stack Overflow is for programming questions. Please use Super User or a hardware forum in future.
The link below says your laptop supports upto 8GB DDR3 1333MHz(PC3-10600) 204-pin SODIMM RAM so get 2x 4GB sticks. As long as you search for “DDR3 1333Mhz 204” or “DDR3 PC3-10600 204” RAM, it’s then primary based on price. Some sites even say it supports 1600Mhz (PC3-12800) and you have that in your system currently.
I put in “ddr3 pc3-10600 1333mhz 204-pin sodimm 4gb” into eBay and plenty came up.
http://tech.firstpost.com/product/laptops/vaio-sve1511aenb-specification-293362.html
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solved Which RAM type should I get for my laptop? [closed]