Hi @west25, I recommend performing a soft reset on your A13 (no data will be lost) by pressing and holding your Side and Volume Down keys together until you see the Samsung logo. Please also ensure you have a strong connection to the internet and that your phone is sufficiently charged. Then, attempt to install the update again.
If you find you're still having the same issue after trying this, I recommend attempting to update via a laptop/computer using the Smart Switch software. Just launch the software > Connect your USB and you'll be prompted to install an update.