Hi all , first post so hope its in the right place , my daughters 5c is due a software update to 8.1.2 , does this update go over the original software or will it be next to it using up even more memory of the 8gb it has , many thanks , Dave
That depends on your method of updating. If you do this using Wi-Fi, it will also need a bit of the storage space on her device, although the update to iOS 8.1.2 is just a minor one, if it's already running iOS 8.1.1. Updating OTA (using Wi-Fi) will not replace the previous software version.
If you use iTunes, this will be different. It will wipe the iPhone completely and install the new software.
If there are apps on her iPhone that she doesn't use, delete them from her device to free up some space. If she needs them again, she'll be able to upload them again from the App Store (Purchased tab).
If she has many photos in the Photos app, it's a good idea to save them somewhere else. Online Storage apps like Box, Dropbox, Google Drive, OneDrive and others are able to upload them automatically, and then she can remove them from the Photo app, which will also free storage space on her device.
In case she opened attachments in the Mail app, this will also add to it's storage space. Delete the account from her iPhone and set it up again, this will reduce the amount of storage for the account.
These are just a few things you can do to get more storage and update her iPhone. And in her case, it's better to use iTunes (computer) to update it.