How to improve bad performers ?

Underperforming employees are not hard to find. They are perpetually tardy or absent, or procrastinate and mismanage projects. They are cavalier about company rules, create conflict in the ranks or seem to do just enough to get by. They abuse the system.
For fellow employees these individuals are a sore thumb, a drag on productivity and a punch to overall morale. 
For the business, they hurt profits and drain management’s time. According to International report , managers spend nearly 17 percent of their working hours dealing with poor performers. 
That’s basically a full day a week that could have been spent being productive.
It is critical that leaders proactively deal with underperformers. 
Experts identify two main reasons employees underperform at their jobs. 
1-Either they lack the ability or skill set required, or 
2-They lack the motivation or desire to perform, or both.
Managers should begin their plan of action by properly identifying the degree to which an employee’s poor performance is due to a “can’t” or a “won’t.”

1. Study: Start the process by studying the employee. Be curious about why they are working the way they are. Document times and dates, and gather concrete examples or poor behavior or performance so you can properly assess whether the issue is due to lack of skill or lack of will. This information can be used to confront the employee and create a strategy for improvement.
2. Strategy: Set a one-on-one meeting with the employee and present your concerns about their performance. Take note of any reasons they give or ways you can help them improve at their job. Review the requirements of their job, and collaborate on a strategy for them to accelerate their performance.  Examples include skill training, education, and mentoring for the “can’t do,” and feedback, concrete goals and new work arrangements for the “won’t do.” Lastly, set a time period and a time to meet back (such as 30 days) and reassess.
3. Review and Decide: After the allotted time, meet with the employee to review their performance. If they have excelled, applaud their efforts and continue with the strategies and structure that set them on the right path. If they have not, but seem motivated and committed to their work, consider moving them to a more suitable position in the business. If they have not performed and are uncommitted to improve, make the tough call to let them go.
4. Be a leader, not a manager: In both cases, avoid seeing the employee as the enemy or fostering an environment that is combative. Great leaders inspire their people. Keep feedback and communication open and positive. Look for creative ways to help your people succeed. One great question every great leader should ask is, “What can I do to help?”

On a final note, consider how your organization is facilitating poor performance. Prevention is much easier (and cheaper!) to implement than treatment. Leaders and management should examine their hiring and retention practices, which directly impact employee performance and motivation. Some examples include better background checks, expanded interviewing and job assessments, more creative recruiting practices, detailed job descriptions and better orientation and onboarding practices.
Plus, employee development and career opportunities should be included in any healthy workplace.  As business strategies and operations change, employees should be given the tools and  skills needed to succeed.