I was wondering if there is a way for me to straighten these thick stems. I'm about to repot it, but I really need it to grow upwards if possible.

No. You can try putting a strong support and tying the plant to that but if you try and bend the stems they will break. This is why Monstera sometimes get 'unsightly' as houseplants. They are meant to climb. In nature they will climb over 30 feet up a tree in the rainforest. They really aren;t meant to be allowed to just grow unsupported in the breeze. This is how they are meant to grow. Hard for a houseplant to duplicate.

It will also help if you move it lower so it gets more light from above.

Thanks for the feedback, it actually is possible to straighten it up. But it needs to be done gradually, I took it to my local garden Center and this is the advice I was given. I've taken the first steps by repotting it and splinting it with a home made moss pole. As it grows towards the light, I'll re-splint it to grow up the pole. I'm already pleased with the results. hurray!

Good!

I just wanted to share this photo showing the progress of my Monstera. It's almost three months since I repotted and splinted it to a moss pole. I've been wetting the moss pole regularly and it's slowly starting to move upwards. I've also used Velcro plant ties so I can easily adjust them to further train the stems to grow upwards. It's working beautifully! :hurray: