When you upgrade your account, it upgrades your account's max knowledge limit.
This does not automatically upgrade the limit for each existing bot, you need to click on the bot's "Edit Details" menu/button and change its knowledge limit to the desired limit.
The knowledge limit is configure per each bot, as some bot's may want to use a smaller database size to improve their performance.
Note, there is no issue with exceeding your bot's max knowledge size. The bots automatically clean their database every night to reduce their size to their limit. This mainly involves delete old conversations and garbage data. Bots will continue to function when they exceed their knowledge limit, they will only stop functioning when they exceed their max knowledge limit by a factor of 2.