Report error: Picklist value des not exist

Hello,

we've been modifying some picklist fields recently.

Now, if I try to run existing reports that used some of those picklists in filters I get the error 

For the filter 3: Picklist value does not exist

I understand the reason.

But, if I try to edit the report in order to correct the filters and use updated values I'm not allowed and the attached pop-up opens.

I'm asked to contact the SysAdmin... but the SysAdmin is me! :-)

Any suggestion?