There are no specific commands for the conversion of non parametric to parametric model. only difference is whether we are making it parametric by using 'sketch based features' (part modelling) or surfacing.
Depending on that your approach gets validate.It varies for supplier to supplier.
Non parametric model has to history of any feature used for its creation. It will be a dump or dead body. It will show a single 'body0' in your part navigator.
For converting it, you need to specify CSYS at such a postion such that its functionality.And then only you can start your modelling.
If you have any doubts feel free to ask.