Enhance risk is one of the strategies for positive risks or opportunities given in the PMBOK, 5th edition, section 11.5.2.2. This strategy involves trying to increase the chances that a potentially positive event will occur. (Remember that a "risk" in project management terms can be a positive event.) In the PMI process framework, sharing the risk is one of the tools and techniques for plan risk responses.
Related: partners, Plan risk management, SWOT, SWOT analysis
Other risk handling strategies are avoid, transfer, mitigate, accept, share, or exploit.