Can SQL Server 2014 Standard Edition Trial be upgraded to a full Core license?

I am adding this answer as it could be helpful in solving sql server 2014 standard and related to Inplace upgrade First you require to check using the link Thomas gave whether the in place upgrade you are doing is supported or not. After you are sure you meet the upgrade matrix you can proceed with two considerations

• If you are upgrading from enterprise evaluation edition to enterprise you do not have to worry and inplace upgrade would likely be smooth.
  
• If you are upgrading from enterprise evaluation edition to standard edition problems can arise. You can use the evaluation edition for 180 days and if you have used any enterprise feature in the 2014 evaluation edition, but upgrading to standard edition, your upgrade might fail (this was a bug in 2008 but still can be noted in 2012) This link has similar information. Even if successful you would lose all enterprise features so you need to plan accordingly.
  

You can query DMV sys.dm_db_persisted_sku_features to see what all enterprise features you are using. select * from sys.dm_db_persisted_sku_features Finally when doing inplace upgrades first please run an upgrade advisor. make sure it does not list out any warnings and errors. After you are done with it you just need to right click on setup file of Version you want to upgrade to it will pop up installation page where you have to select maintenance and then instance upgrade to upgrade to required instance