A couple of months ago, I've backup the android partition and removed it. The built-in drive is much faster than the micro SD (despite I've bought a faster micro SD) and therefore, much better for image capturing for the Sun and planets. However, it has very limit space... in order to maximize the size, today I decided to remove all android related partitions.
To further free up spaces, I've mounted the micro SD to a NTFS folder and then moved the dropbox folder there. So, I will have around 10G more space.
This is to prepare for the partial solar eclipse, as well as future imaging requirements.