Read the Dev blog here. Basically: PLEX will be broken down into more granular portions and AURUM will be removed from the game. All existing Aurum balances over 1k will be converted to the new PLEX and 30 days later, balances under 1k will be converted. AURUM tokens will be removed from the game. Make sure you convert them otherwise they will be lost. The new 'granular' PLEX can be used to buy ship skins and other services. Based on the screenshot, a single current PLEX will be broken down into 500 PLEX. They gave not definite time line for this, but expect it sometime after Fanfest in early April.