How to follow data behavior through time?

Hello,

I have a data set of clients from 4 different years... 2014, 2015 ,216 and 2017 In the data I have divided the client into 3 different groups: Low spending, intermediate spending and high spending. I am very interested in analysisng the behavior of the clients and see how they change their behavior through time. For instance I want to see from the clients in 2014 how many of them became high spending or intermidate or stayed the same and how their behavior was through the 4 years. I do have a client ID number for each one of them and I have made the groups already.

Thank you in advance!

Teo