At the risk of getting another "what does that mean?" response, I'm going to answer this...
You need to add
a condition to your event that compares the current angle with the maximum angle. Like so:
+spriteArm.Angle Greater than -45 degrees
-Set spriteArm.Angle to (spriteArm.Angle-5)
This is just an example, mind you. There are several ways you can do this.
Judging from your recent questions on the forum, you seem to be having trouble with basic things like comparing values and using multiple conditions in your events. Have you read the tutorial? It covers a lot of the basics as far as setting up events and performing actions. I suggest you start there. And don't just read it... do what it says. Make the tutorial game while you follow along. It's good experience.