In which case cisco switch require to upgrade license

[krahulbgp]

 In which case cisco switch require to upgrade the  license   

instead if I upgrade ios  will it work ?

[Richard Burts]

You ask a very broad question without providing any context (what type of switch, what is current version of software, what is current feature set/license, what will be new version of software and feature set/license). I will respond in very general terms: for most Cisco switches and most versions of software, and most licenses/feature sets once it is established and running the license will not need to be upgraded.

[Leo Laohoo]

In addition to @Richard Burts' comments: 

NOTE: 

1. Not all switch models support license upgrade.  For instance, switches with LAN-Lite license cannot be upgraded.  LAN Base license, the "lowest" license, can be upgraded.  
2. SSH/crypto does not require a license upgrade.

The only time a switch's license needs to be upgraded is when there is/are feature(s)/function(s) needed in which the current license is not suffice, such as VSS, routing, VRF/MPLS, etc.