できます= can ( 1. be able to do that generally in informal occasion / 2. be able to do very well in business occasion )
わかります is used with (少し、よく...etc) respectively (a bit , well..etc ) , so if you use わかります , the meaning of it is wide range from a bit to well .
The meaning of できます depends on situation.
If you say ”できます" in business occasion , auditors regard you as you can do it well . so If you can't do that after the declaration in business scene , you will lose belief from your coworkers.
but , Of course , you can use it in informal occasion but if you use it many times , you might be thought as narcissist. so you should use this phrase in appropriate situation.