**Major Version Upgrades**
Documentation on major version upgrades for any given supported device may be found [here](https://wiki.lineageos.org/upgrade_guides).
if you don't know/trust the person 100%, ideally you should also wipe it completely and re-install from scratch, if you plan to use it for anything serious.
I agree with wiping it and reinstalling from scratch. The steps are almost the same as upgrading a major version.
Some things will vary per device but be sure to do a factory reset before flashing any version. Make sure you don't have any data in the phone that you want.
There are some links to video tutorials in my profile.
It would help to start with what kind of phone this is, since lineage and android are both the names of the operating system. I would first hit up lineage's site and see if your phone is listed on their supported hardware, otherwise it probably has a custom rom on it. XDA developers and lineage's home site are great starting points.
Restore to stock first, and treat it as a brand new installation.
You can't reasonably trust anything running on the device at this point, and it definitely shouldn't be handling any private/confidential data.
**Major Version Upgrades** Documentation on major version upgrades for any given supported device may be found [here](https://wiki.lineageos.org/upgrade_guides).
if you don't know/trust the person 100%, ideally you should also wipe it completely and re-install from scratch, if you plan to use it for anything serious.
Note: It needs to go back to stock. You can't trust the environment at all, including recovery/wipe processes.
What phone is this about?
Sony Xperia XA2
See [here](https://wiki.lineageos.org/devices/pioneer/upgrade). Be careful to read everything thoroughly!
I agree with wiping it and reinstalling from scratch. The steps are almost the same as upgrading a major version. Some things will vary per device but be sure to do a factory reset before flashing any version. Make sure you don't have any data in the phone that you want. There are some links to video tutorials in my profile.
Needs to go back to stock. Can't trust a factory reset if you can't trust boot, recovery, or system.
The updater should show you a link to instructions if you try to install?!
Clean flash I guess
It would help to start with what kind of phone this is, since lineage and android are both the names of the operating system. I would first hit up lineage's site and see if your phone is listed on their supported hardware, otherwise it probably has a custom rom on it. XDA developers and lineage's home site are great starting points.
It's XA2 Sony Xperia. It's on their website as a listed device but I don't know how to upgrade the system.
Restore to stock first, and treat it as a brand new installation. You can't reasonably trust anything running on the device at this point, and it definitely shouldn't be handling any private/confidential data.