I assume you are trying to update a socket card already socketed on a gear part (level 40~49 gear) right?
There are socket cars which are level limited - I guess yours can only be socketed on level 40~99 gear parts. Then the upgraded one can be only socketed from level 50~99 gear parts. I also assume you're talking about a stat socket card right? There is an easy rule for them: Socket cards which have stats in percentage values don't have any level restriction. You can upgrade them to the final grade no matter which level your gear part has. The cards with the absolute stats (like HLT +X) are level restricted. The maximum grade of the HLT stat card you can put on lvl. 40~49 gear parts are 4* [Special] HLT stat cars, for a 5* HLT stat card you need gear parts Lvl. 50+.
I hope that was understandable.
Edit:
Since an image says more than thousand words:
If you want to upgrade the card anyways you have to extract it from the gear part and then you can upgrade it. But keep in mind that the new 5* card can't be equipped on the Lv. 40~49 gear part.