I'm probably just being ignorant, but

Well that pc is really really weak. You can be happy with the performance you are getting with it.

[Blackdog_kt]

As already mentioned, you can alt-click on any text/information window to bring it into focus (the reason for the alt-click is to make sure you don't accidentally click them during flight, normal clicking is reserved for operating the cockpit controls) and then you can right click on it and select customize or close.

A bit of advice though, if you disable the windows and decide you want them back at a later point you'll have to create and edit them in from scratch. I think the settings for the windows are kept in the ConfUser.ini file in your documents\1c Softclub\IL-2 Sturmovik Cliffs of Dover folder, so you could back this file up just in case you decide you want them back at some point.