Go to Walkr > Menu > Social > League, then tap Join a League. The system will use your galaxy's population to place you in the appropriate league level.

There are 7 levels:

1. Comet League > Galaxy population: 0 - 199
2. Planet League > Galaxy population: 200 - 399
3. Star League > Galaxy population: 400 - 599
4. Supernova League > Galaxy population: 600 - 799
5. Nebula League > Galaxy population: 800 - 999
6. Blackhole League > Galaxy population: 1,000 - 1,199
7. Galaxy League > Galaxy population over: 1,200