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• Select your branch (see above) as the pull request source (left side).
• Select the current development branch as the pull request target (right side).
• Fill in the Title and Description fields 
• Request Reviewers
• Click Create pull request

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Synchronize with the main repository

If the main development branch changes, you should merge in those changes to your fork. Bitbucket has utilities that make this easy -  see https://blog.bitbucket.org/2013/02/04/syncing-and-merging-come-to-bitbucket/. 

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