Blogger default themes are so boring and also you don't have enough layout customization. That's why you want to change blogger theme that you like.
Here are some steps to change blogger theme
Step 1: Download the theme you like which perfectly suits your blog category
Step 2: It comes with a zip file just right click on it and then click on extract here
Step 3: Go to blogger website, Click on theme and then click on restore and here you will show the upload from computer option, just click on it and upload from extract here files which ends with (.xml)
Step 4: Click on save and boom you will see your blogger theme will be changed
