Thread-safety in C#

Thread-safety in C#

I have currently been assigned a project that was implemented couple of
years ago in C#. It consists of frames and some excel-files extraction,
but the problem is that this project is extremly broken/outdated and I
have to change some functionalities and add some new feature.
There are some libraries that are supported only after .NET framework 3.0
that I need to use in the new features,and the framework that the current
project was built on is 2.0 or less,so changing the framework raised some
thread safety problems.
Between two partial classes for example which are the design file code and
the backend code trying to change one label's value raises an error saying
that I can not edit something that is being used at the moment... I used
delegates for one of the labels, and it worked fine..then the other
textbox raised another error.. So is there an option to encapsulate the
whole thing and apply thread safety to the whole code without having to
follow each line where the error happens?
Regards