Hi my iPhone 3gs is currently operating on 6.1.6.
I'm trying to load an app & when I push install a window comes up telling me I need to update to iOS 7 or later.
My software updates say I'm up to date.... Is there a way to force an update???
The iPhone 3GS is only upgradeable up to iOS 6.1.6, released February 21, 2014. [Wikipedia]
There are ways if you look on the net. Below is a quick copy and paste of one trusted site I use. Most anyone can do this. Just do a search for the files you need to download that are mentioned below. It is straightforward and minimal risk (especially on older phones you are on the fence about upgrading anyways).
Step 1. Backup your iPhone 3GS and remember that you are installing the tool at your own risk. Think twice before you continue.
Step 2. Download Whited00r7 for Windows or Mac and your iPhone / iPod touch model. You can get the program here.
Step 3. You will have a zipped archive with the program and all the tools necessary for the installation process. Unzip the folder.
Step 4. Launch Redsn0w program. You need to select “Extra” option and choose “Pwned DFU” button. The software will show you the guide so, please, follow it and wait till your smartphone is set into Pwned DFU mode [you will see the black screen at this point].
Step 5. It’s time to install Whited00r7 program with iTunes. To do this, you should press / hold SHIFT on Windows PC and point to Whited00r .ipsw file located on your computer.
Step 6. Finish the installation procedure and reboot the iPhone 3GS.