I don't think you can replace the eMMC directly (happy to be corrected if I'm wrong).
You can however, insert a SD card (directly above the SIM card) with as big a storage as you like.
I'm not sure how the different distros handle the SD card (automount, mount when accessing in filemanager),
Mobian f.e. mounts it on access.
Edit: There are
eMMC available in the store, but I don't know if you can actually use those with the PP.
And if you actually can there might be some soldering required.
Maybe have a look at the
schematics.
Judging from the
eMMC datasheet a few options might be available,
but again it might not be that easy to actually "install" the eMMC. I'm also reasonably confident that you would void your warranty
![Wink Wink](https://forum.pine64.org/images/smilies/wink.png)
In case you are interested in disassembling your device, the eMMC is on
the back of the mainboard. It is the U700 thingy