Choose lElk token as the From token on the swap tab & Elk token for the other token to swap to. If you can't see the new Elk token as an option, you can add it by using this contract address 0xE1C110E1B1b4A1deD0cAf3E42BfBdbB7b5d7cE1C
Image 1. Upgrading lElk to Elk - approve.
Enter the desired amount for upgrading and click on Approve Upgrade (1/2) button.
After the approval transaction has been submitted, you can now upgrade the legacy token for the new one with a 1:1 ratio by clicking on Upgrade (2/2).
Image 2. Upgrading lElk to Elk - Upgrade.
After the transaction goes through then you've successfully upgraded your old tokens for the new ones.
Note: Make sure that you will break/exit your current LP pairs, upgrade your tokens and then provide liquidity with the new token.