DerGora :
Thanks to answer.
If I first chage the GPU the CPU will get a drastic bottleneck? or it could be acceptable?
This are the complete specs:
CPU: FX 6300
Cooler CPU: Cooler Master 212 Evo
GPU: RX 480
PSU: AeroCool KCAS-650M
Case: Corsair specs 03
RAM: 8GB DDR3 2400Mhz
MB: Asus 970 Pro Gaming
HDD: 2Tb 7200rpm
System: W10
Drastic bottleneck. The FX 6300 + RX 480 doesn't pair well. Here's a good guide to check which CPU would be ideal for an RX 480:
https://docs.google.com/spreadsheets/d/1qSkGtqIXpBBFwidUxl2LlWpIh3CQQGTrfc4WySMe14o/edit#gid=0 (Source: http://www.tomshardware.com/forum/id-3192807/ultimate-bottlenecking-guide.html).
Also, I highly recommnd to change your PSU alongside the GPU upgrade. Though the KCAS-650 (650W) could provide enough juice to power your rig (at 624W at +12V), the PSU is not a good quality unit (and only has 2-year warranty - which probably has already expired).
I would suggest looking at the Seasonic G-550 (hybrid modular cables like yours, 550W good-quality unit - which is more than enough for your upgrades, and 5-year warranty) or the EVGA SuperNOVA G3 550 (fully modular, same good quality unit, and 7-year warranty) or the Corsair RM550x (same but 10-year warranty).
If I was in your position, I'd start with the CPU-MB-RAM upgrad first. Then the GPU-PSU.