If you already deployed the solution earlier then you don't need to re=deploy whole solution again, instead, you can deploy on the part which got modified.
Let's say, if there is some changes in the class library project, then you just need to build the class library and replace its .dll with the deployment folder.
If you have made some UI changes like in .aspx or in .cshtml, just replace that file to the deployment server as it will not affect other functionality.
But make sure, that it is not affecting other things. Like if you create an additional method in the Data Access layer or in Model and then you are calling it from the Business Logic layer or from controller then you need to replace all those files or dll's which got modified otherwise the solution will not work.
Hope it will be helpful to you.
Pawan Awasthi(DNS MVM)
+91 8123489140 (whatsApp), +60 14365 1476(Malaysia)