How do I man up in a relationship?

 It depends upon the idea of “man" you've in your mind.

If according to you a “man" in the relationship is someone who's superior, dominant to the position of becoming a master to the girlfriend/wife, I suggest you first change the definition.

If according to an Indian woman, you want to “man" up in a relationship, these are some things that you should rather be doing.

• Spend time with her. Talk to her. Communicate with her.
• Tell her about how your day was. Tell her about your fears and tensions. Tell her your secrets and tell her what's keeping you up at night. Gossip about your friends, family, and work with her. And do hear her out when she does the same.
• Remember little things about her. How she takes her tea. How she feels cold in the month of December. How she always forgets her medicines.
• Tell her you love her, and how lucky you're to have her, try it as often as you could. Do you want to bring out the best woman in her? Tell her these things as much as you could.
• Appreciate her for all that she does for you. Just like you always remember scolding or blaming her for her faults, appreciate her for all that she does for you.
• Forgive her quickly for her little mistakes if she asks for one. Ask for forgiveness quickly if you made a mistake.
• Stand by her like a rock. Don't ditch her in the worst of times.
• Accept her for who she is. You cannot crib, nag, throw tantrums, become violent to change a lady. She'll change herself according to situations and out of love. Never out of power or fear. If she fears you, you've already lost her as a woman.
• And if you really want to man up, treat her as an equal. She isn't your boss, your employee, your employer, your colleague, your work friend, your maid, your relative. She's your wife, she's your girlfriend, she's the best friend you'll ever have if you both try truly.