Lightroom 6 cannot be reinstalled

your lightroom 6 is an upgrade from a previous version.

when you start to install, you'll be prompted for your lightroom 6 serial number. you will then be presented with a dropdown that allows you to select the qualifying version (eg, lightroom 5). select the qualifying version you own and then enter its (eg, lightroom 5) serial number.

enter the correct number at the correct time and installation will proceed.

if you need help finding a serial number, there are several possible ways to find/recover an adobe serial number.

1. search purchased materials: https://helpx.adobe.com/download-install/kb/find-serial-number.html

2. you can check your account (if you purchased from or registered with adobe AND you remember the adobe id used to purchase/register), https://accounts.adobe.com

3. if your adobe program is installed on another computer you can recover its serial number from that computer,

(win:) http://www.belarc.com/free_download.html

(mac:) https://mac-product-key-finder.com/

A qualifying product is a previous version of Lightroom.

You bought an upgrade to Lightroom 6, and are asked to enter serial number for the version you upgraded from. (or from any previous version you have bought)

If you registered this version with Adobe, the serial number can be found in your Adobe account.

If you didn't register it, it may be possible to find the serial number  on your computer if that version was previously installed.

If you have a disc with Lightroom 6.0, you can download the latest version, 6.14, from this page:

https://helpx.adobe.com/lightroom-classic/help/lightroom-6-end-of-support.html

Are you on Mac or Windows?

If you have a Mac with a recent OS, you might not be able to install LR 6 because it uses a 32-bit installer, but there are apparently workarounds.

You have posted in Using the community, which is for issues with the forums themselves.

A moderator should move this thread to the Lightroom Classic forum.