Server is slow,Deleted users still in GAL,Low disk space in Admin GUI

[chacetech]

Iam new to this so any help will be greatly appreciated.
I am using Release 5.0.1_GA_1902.UBUNTU6 UBUNTU6 FOSS edition
I have approximately 250 users and recently been getting users complaining that the server reports it is slow cancel request. The network is all on 1 gig ethernet LAN and the server is a good HP Proliant with 10 hot swappable hard drives with 164gig each. Will the latest update 5.0.20 fix some or all my issues? Also please can you tell me how and when to update to the latest update. I was also reading that you can run a script optimizeMboxgroups.pl . Where do I get this script from?
I deleted users in the admin console but their aliases are still in the GAL. How do I delete these aliases.
On my Admin Gui it shows with very little disk space but on CLI it has says 35% is free. Even after me deleting some 20 users it shows the same in Gui and CLI.
Thanks for any help