You being a System Administrator, will know more about how to create or architect certain things. You can choose your career accordingly.
If you go for testing, you will need to have experience in Testing i.e. Manual or using selenium etc.
If you opt for Cloud Computing, your experience as a System Administrator will surely count. You can also opt for taking a certification examintaion by AWS or Azure or GCP for Cloud Architect, this surely will give you an added advantage.
You can also look for some online courses:-
Cloud Computing:- https://www.edureka.co/cloud-computing-certification-courses
Software Testing:- https://www.edureka.co/software-testing-certification-courses
Feel free to ask any doubt you have. All the best for your career.