The sum of the file size for all data files has to be < 10 GB, not the amount of data in the file. So, deleting data from some tables, or even dropping some tables, does not solve problem. You need to shrink the file, something like this:
ALTER DATABASE mydb MODIFY FILE (name = N'logical_name', size = 2048MB);
This will fail if the database size can't be reduced to 2 GB. You may need to first issue:
DBCC SHRINKFILE(logical_name, 2048);
If you use any form of SHRINKFILE, then you'll need to validate in File Explorer that the data file(s) are actually as small as you think (because shrink operations will shrink as much as they can, and stop silently when they can't reach your target size).
Then take a backup, then restore on SQL Server Express (with @@VERSION the same or higher than the source, of course).
You may come across other issues, for example if you have used any features that aren't supported on Express.
No you cannot do inplace upgrade from SQL server 2008 R2 express to SQL server 2014 developer edition. Its not supported as per Version and edition upgrade supported matrix
You can only upgrade to below using inplace upgrade method
SQL Server 2014 Enterprise
SQL Server 2014 Business Intelligence
SQL Server 2014 Standard
SQL Server 2014 Web
SQL Server 2014 Express
But there is other option to do side by side migration. You install SQL server 2014 DEV edition. You backup your user database from SQl server express and restore it on SQl Server 2014.
You can migrate logins using This support article
Best Answer
You will not be able to restore a database from Microsoft SQL Server 2008 (paid version) to Microsoft SQL Server 2014 Express (Free version) due to its database file limit.
For others who need reference
SQL Server Express versions have a hard size limit on the database size.
I have listed them below from 2000-2008_r2
Please upgrade to SQL Server 2014 (Paid version) to resolve this issue.