speed up Synology NAS file server for very large excel files

I am looking for a freelancer who can help me speed up my Synology NAS file server for very large excel files. I am using a DS218+ model and typically work with excel files ranging from 10MB to 100MB in size.
1 file freezes the PC when trying to open from the NAS in Windows.
Skills and experience required:
- Experience with Synology NAS systems and optimization
- Knowledge of techniques to improve file server performance