If you want to do this on a regular basis, consider setting up an event with the paycheck action.
If you want to do this manually, go to the user manager in vbcredits and select the usergroup you want. Open the advanced options and look at the formulas. To add an amount to everyone (say 100, and assuming your currency is Credits), then your formulas look like [Credits]+100
Then click update users and they will all get 100 added to whatever they had. Click through to the next pages and just click update users each time (the formula settings will remain between pages)