Error discovered in an accepted conference paper but not yet presented
Talk to your co-authors of course. But also talk to the conference committee and provide, or offer to provide, corrected copy. They may be able to help or not. But for the presentation, give the latest, most correct, version and note, if necessary, that the printed version has small errors not affecting the conclusions. 

Some CS conferences will print proceedings and some of them will have a version ready before the conference. It may be possible that a second version, for general distribution, can differ a bit in details, but that is up to the conference and to the publication board of the organization sponsoring the conference. 

But letting everyone know immediately is the best overall strategy.