I was playing LoL on Garena for 1 year.Then I wanted to change my region and I knew I can't transfer my account to Riot server. So I created an account on the Lol official website,and downloaded the installer etc. The problem is...I don't want to download another folder of LOL files on my computer. Can anyone help me to let my Oceania client use my Garena lol files to play?
Short answer: No, it is not possible.
Long answer: No (see below).
Garena and Riot don't share the same client, even if the codebase of the related files are similar. This is because they run on completely different environments - one uses the Garena client and the other uses the Riot launcher, which is what you see on the login screen. So that's one difference already - the login procedure is completely different. And that is one reason why it is incompatible, along with other reasons like localization and not running on identical patches.