You can found download link button of LineageOS 14.1 for Galaxy Ace 3 LTE can be found from below but it is required to check some requirements in case you do not want to face with any issue during the installation process.
Requirements and prequisites
This tutorial is supported only with the Samsung Galaxy Ace 3 LTE devices. Don't aplly these rom and guides onto another devices.
Make sure you’ve rooted and installed TWRP Recovery on your Galaxy Ace 3 LTE. You can using other recovery as well, but I prefer TWRP for thr better.
In order to correctly install this Nougat ROM you will need to wipe the data and factory reset your Galaxy Ace 3 LTE. This step is included in the guide and it means that you will have to backup all your files using cloud storage services, a SD Card or a PC.
Important to noted: don't back-up and recover your app and data using Titanium Backup app. It will cause serious issue later on.
Make sure that your smartphone’s battery charge level is over 20%. This will prevent it from powering down while you’re upgrade Galaxy Ace 3 LTE to Nougat 7.1.1 using Lineage OS ROM.
1. Download LineageOS 14.1 for Galaxy Ace 3 LTE Nougat 7.1.1
This is major update, wich is have bigger file to download the rom. You better connected your Galaxy Ace 3 LTE to strong and stable WiFi network to be able to download wuthout corrupting the rom file.
Remember to download the latest version if there were newer build of Lineage OS 14.1 to experience better performance.
2. Donwnload Nougat Lineage 14.1 Gapps
Since, you are interested to update your Galaxy Ace 3 to Android 7.1.1 Nougat using a custom ROM with LineageOS 14.1 ROM, you also need to download and flash compatible Google Apps in order to be able to use any Google services. If you don't need it, just leave it.
Chose pico arm/arm64 for the smallest package.
3. Installing LineageOS 14.1 on Samsung Galaxy Ace 3 LTE
As you've been downloaded both the Lineage OS ROM and Lineage Gapps from links above, then transfer them to your phone's internal storage.
Now you need to power off your Samsung Galaxy Ace 3 LTE completely, don't enable quick boot.
Next step is to boot it into TWRP Recovery mode. Use the hardware button combination.
Now the first thing you need to do once, you are into TWRP Recovery main menu is to perform a factory / hard reset. From the TWRP main menu tap on the wipe button and swipe to the right side to complete the operation.
Next, tap on the install option from the TWRP main menu and just pick the Nougat Lineage OS ROM for Galaxy Ace 3 that you’ve downloaded before, which is saved to your phone’s internal storage and install it by swiping to right of the button (swipe to confirm). Wait the procces done. Don't reboot to system yet.
When the Lienage OS custom ROM is successfully installed you can install the Lineage OS GApps package, right after the custom rom.
In the end, reboot your Galaxy Ace 3 LTE to system. It will take some time before it works nornally. Follow the setup wizard appeared.
Now you're done.
This is easy peasy, isn't it? You already know where you can download Lineage 14.1 for Galaxy Ace 3 LTE custom ROM which is based on Nougat 7.1.1 OS and How to install it for you Galaxy Express. For any questions or help use the comments section.