It looks like the branch management (one of the admin settings) in bitbucket has been configured to only allow certain people to push directly to master.
Try creating a branch – git checkout -b test, create your test commit and push git push origin test:test. You can always cleanly delete this branch once you have completed the test.
The other option (probably best agreeing with whoever set this up) is you go to bitbucket and head to admin, branch management and remove master be too limited. cf – https://confluence.atlassian.com/display/BITBUCKET/Branch+management