I found a great post from : SharePoint: How to shrink transaction log file and
I was able to follow the instruction and successfully shrink transaction logs for SharePoint database without any problem. 

Here is the instruction to shrink transaction logs  files for SharePoint

1. Change the database recovery model to SIMPLE using the next command:
   • ALTER DATABASE SET RECOVERY SIMPLE;

     

2. Shrink the database or transaction log file using Microsoft SQL Server Management Studio:
   Right click on the database which you  altered to recovery simple and go to Task | Shrink | Database  It will take some time depend on on the size of database

   
   Or use the following command to shrink the transaction log file, for example, to 5 MB:

   • DBCC SHRINKFILE (_Log, 5);
3. Set back the database recovery model to FULL using the next command:
   • ALTER DATABASE SET RECOVERY FULL;

     

If it’s not production database, you, in principle, can skip step 3 leaving the database recovery model in SIMPLE. Transaction log in this case will not grow. But note that some people complain that it can cause some problems while attempting to delete SiteCollection from SharePoint Central Administration. I’ve never been faced with such issue, but just in case keep FULL recovery model.