What is the procedure to change Baseline plan of the project? When do you considering changing Baseline plan of the project. Who need to approve the baseline changes?
The procedure to change a baselined project plan is whatever your change control procedure is. You should not change a baselined document (plan, schedule, budget, whatever) outside of your change control process.
The change control process should define things like who has the authority to approve a change, how a change is documented, how a change is communicated to the team, etc. This should be documented either in your project plan or in documentation that your project plan can cite.
There are a number of conditions that can trigger a change. Typically these are changes to scope/schedule/budget that you intend to make. What is not included are things like budget or schedule overruns, in other words deviations from the plan that were not intended.
When it comes to who approves changes, define these upfront based on project needs. You will want to set a threshold of authority for e.g. the PM, project sponsor/champion, corporate management etc. For example, maybe the PM is allowed to authorize changes to the budget up to a total value of $10,000, the project sponsor can authorize up to $100,000, while more costly changes have to be approved of at a VP level.