This study reports the experimental discovery of multi-step topological transitions among various meron and skyrmion crystal states in the centrosymmetric magnet GdRu$_2$Ge$_2$. By performing detailed magnetic structure analysis using resonant X-ray and neutron scattering experiments, as well as electron transport measurements, the researchers found that the compound hosts periodic lattices of elliptic skyrmions, meron/anti-meron pairs, and circular skyrmions, with diameters as small as 2.7 nm. These transitions are well reproduced by a theoretical model considering the competition between RKKY interactions at inequivalent wave vectors. The findings demonstrate that even a simple centrosymmetric magnet with competing interactions can support a rich variety of nanometric magnetic quasi-particles with distinct symmetry and topology, whose stability can be tuned by external stimuli. This work highlights the potential of GdRu$_2$Ge$_2$ as a material platform for realizing and manipulating a diverse array of magnetic quasi-particles.This study reports the experimental discovery of multi-step topological transitions among various meron and skyrmion crystal states in the centrosymmetric magnet GdRu$_2$Ge$_2$. By performing detailed magnetic structure analysis using resonant X-ray and neutron scattering experiments, as well as electron transport measurements, the researchers found that the compound hosts periodic lattices of elliptic skyrmions, meron/anti-meron pairs, and circular skyrmions, with diameters as small as 2.7 nm. These transitions are well reproduced by a theoretical model considering the competition between RKKY interactions at inequivalent wave vectors. The findings demonstrate that even a simple centrosymmetric magnet with competing interactions can support a rich variety of nanometric magnetic quasi-particles with distinct symmetry and topology, whose stability can be tuned by external stimuli. This work highlights the potential of GdRu$_2$Ge$_2$ as a material platform for realizing and manipulating a diverse array of magnetic quasi-particles.