DO NOT DO THIS UNLESS YOU HAVE GOOD SOLDER SKILLS!
YOU CAN DESTROY PCB PADS AND BRICK YOU DEVICE!
TRAIN ON BROKEN HARDWARE FIRST!
Find a PC3200 DDR 512MB PC memory with 8 TSOP-66 chips on it (Each chip has 64MB size and 8M x 4bank x 16bit memory organization) or 256 SODIMM with 4 memory chips. You should use only 4bank x 16bit memory chips! You are lucky if you got 16M x 4bank x 16bit (128MB) chip - use it! (NOTE: You typically need to match the manufacturer of the memory chips, with the exception of cross-branded chips, for example Hynix/Winbond, as used in this article)
Desolder all chips using rose alloy
Desolder chip from DIR-615 pcb and solder new one. Here is the list of operations:
Tools and materials:
This is photo of original memory chip:
Rose alloy melted to lower melting point temperature:
Old original 32MB chip desoldered:
PCB pads cleaned using soldering iron & cotton swab:
New 64MB chip soldered (use a lot of good flux and clean it after soldering)
There is no need for software changes. Original u-boot detects memory size automaticaly. Just double check your soldering for shorts and other defects before powering up device.