1) When players play matches they will improve their AI. When the AI is 100% the 8 attributes of the player will be 25% higher than when AI is 0%.

2) You can inject more DNA to improve the player. There are 8 slots to inject DNA strands into. The more DNA you add the more the player will improve.

Note! The better - meaning the more rare - DNA you inject, the higher the players attributes will be.

3) When you reach the Super League level (when you promote from League Level 5) you can also overclock your players. Overclocking means injecting a 9th to 12th DNA strand. However note that there is a penalty on the players energi (match minutes left to play in career) when you overclock. So think twice before doing it.

4) Last thing you can do to improve the players attributes is to attach player items to them. When you add items the players attributes will also increase.