Android Phone taking up more space than it should
Theres a few problems it could be (or a combination of):
1. The stock software is massively huge and htc has a problem that an update will fix.
2. An app youve downloaded has installed Bloatware and clogged up your storage
3. An app youve downloaded assumed you wanted to download other things (photos videos ect) without telling you

Id advise

https://play.google.com/store/apps/details?id=com.mobile_infographics_tools.mydrive

To determine exactly what it is that is taking all that space. Happy hunting!