Rockstare Games announced, that players who already played GTA 5 on PS3 or Xbox 360 will be able to transfer their characters and game progress in the new versions for PS4 and Xbox One.
How to do:
“You will need a Rockstar Games Social Club account linked to the console accounts used when previously playing GTA Online.
When entering GTA Online, you will be given the option to transfer your previous GTA Online character and progression data. Once you have chosen to transfer your previous character and progression data, the transferable in-game money, RP and Rank of all previous characters will be displayed. These are the characters that will be transferred to the PlayStation®4 or Xbox One. Once the transfer has completed, you will be prompted to choose a character and enter GTA Online.
You will still be able to play your existing characters on PlayStation®3 and/or Xbox 360, however any progress made with versions of the characters on those systems after a transfer will remain on those systems only. Any existing PlayStation®4 or Xbox One GTA Online character and progression data will be replaced by the previous character and progression data during the transfer, except for any existing in-game money, which will be combined with your transferred balance.
All earned in-game money will transfer. Purchased in-game money that has not yet been spent will only transfer within a console family (e.g. PlayStation®3 to PlayStation®4).”
Source: Website Rockstar Games