I installed B4A 7.8 on one of my PCs. Then I followed all the steps outlined below to update the API version:
1. Tools - SDK Manager.
2. Download SDK. It will open the browser. You should download sdk-tools-windows.
3. Unzip it in a folder such as
C:\Android
4. Set sdkmanager.bat in the SDK manager tool. It will be in:
C:\Android\tools\bin\sdkmanager.bat
5. The recommended items will be checked. Click on Install Selected.
6. Yes and No buttons will appear from time to time when you need to accept licenses. Read and accept.
7. Configure the IDE to use the new SDK. Tools - Configure Paths. Set the path to android.jar. It will be:
C:\Android\platforms\android-27\android.jar
jdk1.8_151 is inatalled
It seems to install everything, but I cannot find Android-27.