You can't change the resulted hash because it's a representation of the content of the file, but what you can do is to put your files in a directory and add the directory recursively to the IPFS using
ipfs add -r <directory name>.
this way the root directory will get its hash from its contents and your files will preserve their name.
First of all, you are not uploading anything, but you are announcing to the network that you have some specific files that you want to share. Then, when another person requests your file from the network, he/she will be connected to you and download the file from you (which means you will upload it to that him/her).
The format of your file remains the same, nothing changes.