As previously suggested, the PDB is a textual file. You can open it and make all the modifications you need. Be careful not to misalign the columns to avoid disrupting subsequent calculations.
If you have Gromacs installed, you can renumber the PDB file using the command: gmx editconf -f file.pdb -resnr starting_number -o output.pdb
Replace file.pdb with the name of your PDB file, starting_number with the desired starting number for residue numbering, and output.pdb with the desired output file name.
In PyMOL, you can use the "alter" command to change things like chain labels, residue numbers ect. https://pymolwiki.org/index.php?title=Alter&redirect=no