To face this type of problem upgrading your project . try to flowing instruction to solve

Error:The project is using an unsupported version of the Android Gradle plug-in (0.7.3).
Starting with version 0.9.0 incompatible changes were introduced in the build language.
Please read the migration guide to learn how to update your project.
Open migration guide, fix plug-in version and sync project

Warning:’android’ is deprecated; use ‘’ instead
To fix it, open file called build.gradle change apply plugins to

apply plugin: ''

Warning:(4, 22) Old buildToolsVersion 19.0.1; recommended version is 19.1.0 or later
Because your gradle plugin version and building tools are not match or old that’s why show this error . to fix it try to change your buildToolsVersion updated

 compileSdkVersion 20
    buildToolsVersion '20.0.0'

Warning: Avoid using + in version numbers; can lead to unpredictable and unrepeatable builds


To fix it, open file called build.gradle change one line not using + blow are sample

    dependencies {
        classpath ''

Error:You must use a newer version of the Android Gradle plugin. The minimum supported version is 0.12.0 and the recommended version is 0.12.2
Error:The SDK Build Tools revision (19.0.1) is too low for project ‘:app’. Minimum required is 19.1.0

dependencies {
        classpath ''

To fix it, open file called build.gradle
in the project root, and change gradle version there to 0.12.2.