My bike suspension is very stiff how can I make it looser
This is a bso. 



The suspension is there just for looks, not for actually doing anything useful, and you don't really have adjustment on it, or the ability to lock it out. That is, you can't do anything. In your case, you want to make the suspension stiffer not looser to reduce the bouncy-ness. That is, if the suspension was fixed, it wouldn't bounce so much. 

In general, suspension costs money to do well. You're looking at ~400-500 USD for bicycles with basic servicable suspension forks, and ~1500+ USD for bikes with acceptable full supsension. 

Decent suspension forks will have some adjustability, and possibly the ability to lock out (i.e. act like a rigid fork). Rear suspension systems of the coil type need a different coil (with a larger spring constant for more rigidity) to adjust significantly. Other types have other adjustments. 

Note that for riding on the road, you don't really need suspension (for comfort, larger tires are often a better choice). And the suspension on your BSO won't really cope with any non-trivial rough stuff off road (note that these bikes are sold typically with stickers saying not to use them off road).