US Cellular and Sprint have started rolling out Android 2.3 updates for HTC Merge and Optimus S respectively. These Gingerbread updates bring improved power management, UI refinements, more control over apps, improved text interface, and refined copy/paste functionality.
LG Optimus S update is available OTA, so you will have to just wait for the notification on your device and then you can complete the update process. However, if you want to manually trigger the process, then go to Menu>>Settings>>About Phone>>System Updates.
On the other hand HTC Merge Gingerbread will have to be completed via RUU, and you will need HTC Sync installed on the computer. You can grab the download from here.