Hey, so you have 256MB of RAM meaning you have a Liquid A1.
Acer has not officially released 2.2 for this phone HOWEVER there is an easy way to flash the Liquid E ROM onto the Liquid A1 and everything (all hardware) works well. Note that doing this does not root your device but does void your warranty (though if your device works and you need warranty repair, best way would be to re-flash Eclair AAP-GEN2. However, I do not think that there is still warranty for a phone this old, not entirely sure tho).
Go to this site and find 4.002.14.EMEA (for Liquid 256MB). It should be near the bottom.- Acer Liquid and Liquid E ALL ROMs bin extract collection - Android @ MoDaCo
Follow this tutorial to flash the .bin file- [TUTORIAL] How to flash .bin files on Acer Liquid/E - Android @ MoDaCo
If anything goes wrong, refer to this - [TIP] Dont try to restart phone during flash if it looses connection, or u will have a bricked liquid! [MOD PLEASE STICKY!] - Android @ MoDaCo
(infact, read that before you begin imo).
And that will get FroYo on your phone. Btw, on first boot, the phone will boot into Acer UI. Play around with it, see if you like it, and if you do not go into Settings-->Applications-->User Interface-->Android UI to switch back to standard Android UI.
Also if you are interested in rooting the device afterwards, check out this Ultimate Liquid Guide by Dario- The ULTIMATE Liquid thread - Android @ MoDaCo
Best of luck.