Removing stock and the effect of the action

Hi There,

We intend to start a 3rd party app called unleashed.

To use the apps we are advised to erase whole stock and add the current one and whole the future stock through the unleashed app.

Can you please help me to understand how to remove the stock and  what could be the effects of removing the whole stock and on the 2nd step uploading it via unleashed. 

Many Thanks

Riza