へ is almost always interchangeable with に, but not vice versa. へ points a direction more than に. に points a destination more than へ. So I recommend beginner students to use に because に is more useful and you won't mistake. (I know you are not a beginner. It's just an example.)

へ indicates destination, and に indicates direction. So in your examples, the literal meaning would be: 東京に行きます = I'm going (in the direction of, "but could potentially get sidetracked on the way to" etc.) Tokyo 東京へ行きます = I'm going (directly to) Tokyo But yes, they can be interchanged readily, and people will still understand what you mean! So I wouldn't worry too much about this one, unless there is a potential for pit stops and you want to specify that.

へ　は　物　ようす　など　動き変化の向きを　言うとき　使う　（　he just use and jshow in condition change and direction )また（other hand） に　は　ばしょ　や　時間や　ひとつ位置　や　一つ点　を　言うとき　（　ＮＩ　is　show and use the piont of time , prace , object )　　Ｃａｓｅ　parical

preposition is the most difficult part of Japanese...