[Help] Crtitical Hit Damage

Good day all, I am preparing to DM my first game in D&D 5E and like all DM's, I have some alternate rules I like to play. The one I'm having issue with is critical damage. The problem is as follows: I use the standard 5E SRD Sheet as that is the one I am accustomed to on Roll20. When a player hits for critical damage, they roll twice and add the modifier. How I want to play (and how I play in my home game) is to have the first dice roll maxed and roll 1 time. (ie: Barbarian crits with Greataxe. Damage is 12+roll+modifier). This adds some excitement because nobody wants to roll double 1's on a critical hit. It also some danger as the enemy can do the same thing. Can somebody help a Roll20 noob DM out here?  Thanks!

Ok, I figured it out and it was very simple. So in my silliness, I'll explain what I found out. Once you bring a weapon from the compendium into the character sheet, you need to edit the weapon by clicking the cog wheel. From there, you edit the "crit" field to the max number of the dice rolled. On a crit it will read as followed (I'll use the Greataxe again as an example) 12+(1d12+Modifier) ie if the dice roll is a 7 and the modifier is a 3 it will read: 12+10. You have to do the math from there. 22 damage.

Great! thanks for posting the answer, in case others have the same question.