If you're having issues installing Windows 10 Builds 10041 or 10049 due to errors about disk space, there's a potential fix.
According to a recent Windows Insider forum thread, there is a bug in how Windows 10 builds are downloaded. Every available language pack is included in the download, which can cause disk space to fill up beyond capacity in some situations, particularly those devices with limited capacity already.
There must be at least 2.5GB of disk space. Microsoft provides the following potential fix:
If you want to reclaim the extra disk space from the language packs after installing the latest build:
Open a command prompt as an administrator
Bring up the interface for uninstalling language packs by typing the following command and press Enter: Lpksetup /u
Select the language packs you want to uninstall.