It's magento 1.9.2 can you guide which block/file i can edit to change title/label of related products?
you can use Magento template path hints to find the related file.
Log into the magento back-end admin
Go to System -> Configuration in the main menu
Go to Developer on the bottom left under ADVANCED
Switch to the store view on the top left to your current website or store view.
Under the Debug tab of the same Developer config page you will see a new option appear that will allow you to turn on/off template path hints.
you can find more details in link
also if you have SSh , you can search the word "related products" using command fgrep -r "related products"