Looking to see if anyone else has done a similar upgrade and how it has worked out.
I've been looking at upgrading the internal flash on my ASA5510 as it's only 64MB. I tried the procedure below on the backup unit and it looks to be operating just fine, but now with 2GB internal and 2GB external compact flash. The cards I used were SanDisk ExtremeIII 2GB CompactFlash. Figured I'd stay with SanDisk as the original card is SanDisk as well.
ASA5510 internal flash upgrade:
Connect to serial console 9600/8/n/1
Save activation key from current system
"show version" and save to text file.
Insert new compact flash card into current system external slot.
Format the new external compact flash card.
Save the current running config to external flash.
"copy running-config disk1:/running-config-saved"
Save the current asa and asdm images to external flash.
Shut down asa and swap in the new compact flash card.
Start the asa.
Connect to serial console and enter the saved activation key.
Copy the saved config to the startup config.
"copy disk0:/running-config-saved startup-config"
Write to memory.