Can't get stand offs- off

There were some stand offs already screwed in ....very very tightly, how can I get them off, all i have is a phillips head, should I buy pliers? or there is some kind of hack

If the standoff is hex shaped find one of these. The name escapes me, but this gets rid of stand-offs really well.

Pliers will work too, just take your time, don't want to strip the threads.