SSH is enabled on the Stratux image by default, so if you're familiar with ssh you can log into the Pi with user pi password raspberry. Then type sudo raspi-config and select the option to expand the card. (It may have been moved to the "Advanced" option).
Another alternative is to connect an HDMI monitor (tv) to the HDMI port on the Pi, connect a keyboard and mouse to the USB port(s), and power up the Pi. On the screen you see a bunch of stuff scroll up the screen as it boots up, and eventually you'll be at a prompt. Log in with user pi password raspberry. Then type sudo raspi-config and select option (one?) and you're done! Exit/reboot and the partition will be expanded. I suggest using an 8G card, as the original image nearly consumes a 2G card already, so expanding it doesn't buy you much additional space. If expanding the card renders it useless, it was a counterfeit card and you can get a genuine one at WalMartWalMart. I use the SanDisk brand.
From https://elinux.org/RPi_raspi-config :
Using raspi-config
It has the following entries (this is the layout from raspi-config version 20160108, January 2016). It may be different on other Raspbian images:
Raspberry Pi Software Configuration Tool (raspi-config)
1 Expand Filesystem Ensures that all of the SD card storage is av...
2 Change User Password Change password for the default user (pi)
3 Boot Options Choose whether to boot into a desktop environ...
4 Wait for Network at Boot Choose whether to wait for network connection...
5 Internationalisation Options Set up language and regional settings to matc...
6 Enable Camera Enable this Pi to work with the Raspberry Pi ...
7 Add to Rastrack Add this Pi to the online Raspberry Pi Map (R...
8 Overclock Configure overclocking for your Pi
9 Advanced Options Configure advanced settings
0 About raspi-config Information about this configuration tool
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