Rajitha,
I am afraid there is not enough information to understand the issue.
Can you please give us some more information ?
1. Please share the MyEclipse Installation Details from MyEclipse > Installation Summary > Installation Details.
2. Where exactly are you trying to set the compiler compliance to 1.8 ? If you are trying to change the compiler compliance for an existing project from the project > properties > Java Complier, then you should uncheck the ‘Use compliance from execution environment on the Java Build Path’ option to be able to change the level.
3. If you are still seeing issues, please let us know what exact steps you are following along with the screenshot of the IDE to help us get a visual.
Let us know how it works for you.