you will need to upgrade the memory/flash to 2Gb
http://www.cisco.com/c/en/us/td/docs/security/asa/compatibility/asamatrx.html#pgfId-48034
If this ASA is in production I would suggest following the upgrade path as mentioned in the following document:
http://www.cisco.com/c/en/us/td/docs/security/asa/asa91/upgrade/upgrade91.html#93962
Upgrade to 8.4(6) and then to 9.1(5)
You could upgrade directly to 9.1(5) but then you will need to enter your configuration manually. The upgrade path is in place to automatically convert any configuration that requires it. from 8.4 to 9.1 there aren't many major changes as there was from 8.2 to 8.3. So, unless you have some really non standard configuration, you should be fine.
I would also suggest going through the 9.1 release notes just to make sure that there are no features, caveats, or system requirements that might cause you some issues.
http://www.cisco.com/c/en/us/td/docs/security/asa/asa91/release/notes/asarn91.html#pgfId-324358
--
Please remember to select a correct answer and rate helpful posts
--
Please remember to select a correct answer and rate helpful posts