CONFSERVER-39659 answer is a cop-out

[JILL C ARNSON]

If a file appears to be "deleted", you cannot upload another file of the same name.

One should be able to either 

• Actually delete the file, or
• overwrite what is currently there

[Mikael Sandberg]

If you read the comment you can see that this is not and issue with Confluence itself, it was cause by Arsenale Lockpoint, an app that allows you to add check-in and check-out capabilities to Confluence, so you can lock any Confluence attachment while making changes.

[JILL C ARNSON]

There does not appear to be any dropdown what lets you "checkout" a document.  Or if there is, it is very obscure.

[Mikael Sandberg]

Arenale Lockpoint is an app you have to install in addition to Confluence, so if you do not have Lockpoint installed then you will not have this option.