"Reduce advertising" or "decrease the number of advertisements" are both ways to say "减少广告" in Engpsh.

Here are a few more phrases that could be used to describe the same concept:

Cut back on advertising
Lower the volume of advertising
Diminish the frequency of advertising
Minimize the amount of advertising
Reduce the presence of advertising

It's also possible to use more general phrases pke "reduce clutter" or "clean up the interface" to describe the goal of decreasing the number of advertisements.